Frequently Asked Questions

Below you’ll find definitions and answers to the some of the most common questions about COVID-19.

We start with the basics, and answer questions about the virus and the disease itself. Next, we dive into SARS-CoV-2 testing and antibodies and what these mean for our immunity following an infection. We also take some time to breakdown exactly what serosurveillance and other population-based studies are and how their results, when allowed to inform the rollout of vaccines, will be critical to Canada’s response to the COVID-19 pandemic.

If you can’t find the answer to your question, feel free to contact us.

About the Virus and Disease

Figure 1.1. Rapidly spreading variants are being observed globally. Some mutations confer potential selective advantages to the virus, such as increased transmissibility or immune evasion. Photo Credit: Mariana Bego.

The name coronavirus is derived from the Latin corona, meaning “crown.” This refers to the characteristic “crown” shape of the virus’ protein spikes.

This viral family has several members that can infect humans: four are potential causes of the common cold, while the others, SARS-CoV, MERS-CoV and SARS-CoV-2, have triggered dangerous epidemics. SARS-CoV-2 is a close relative to SARS-CoV, which was responsible for the severe acute respiratory syndrome (SARS) epidemic of 2002–2003, which infected over 8,000 people worldwide.

The morphology (shape) of coronavirus is depicted here with spike proteins (red) that form a corona (crown) around the virus. Additional proteins shown include envelope (yellow) and membrane (orange) proteins. Photo Credit: Alissa Eckert, MSMI, Dan Higgins, MAMS.

SARS-CoV-2 variants occur when there are changes or “mutations” in the original virus’ genetic code. These changes occur naturally over time as a by-product of replication.

For example, the B.1.1.7 variant was first identified in the United Kingdom where the mutation occurred on the receptor binding domain (RBD) of the spike protein at protein 501, and the amino acid asparagine (N) was replaced with tyrosine (Y).
Other variants have been identified, including the B.1.351 lineage that originated in South Africa and the P.1 lineage that originated in Brazil and Japan.

The SARS-CoV-2 variants are of concern because they appear to spread much faster and may impact the effectiveness of vaccines and therapeutics (medicines to help cure and soothe COVID-19 patients).

Figure 1.2. Rapidly spreading variants are being observed globally. Some mutations confer potential selective advantages to the virus, such as increased transmissibility or immune evasion. Photo credit: Mariana Bego.

Figure 1.3. When a person is infected with the virus such as SARS-CoV-2, the virus replicates many times in the host (humans). These viruses can be passed on from person to person through respiratory droplets (sneezing and coughing). With rapid virus replication and immune pressure to control the virus, this can cause the virus to mutate, generating a new variant. If the mutation found in the variant confers it some advantage, it will spread better in the population. Photo credit: Mariana Bego.

SARS-CoV-2 is the virus that causes the disease known as COVID-19.
Researchers are currently investigating this question. Research suggests prior coronavirus infections may result in the development of antibodies that fight against SARS-CoV-2, but these antibodies may not be strong enough to prevent COVID-19 infection.
Like with seasonal coronaviruses that cause the common cold, recovery from an initial infection gives a degree of immunity and protection towards re-infection. However, some patients who have recovered from COVID-19 have caught the virus for a second time.
COVID-19 causes diverse degrees of illness, ranging from asymptomatic infection (no symptoms) to mild symptoms, to severe pneumonia, strokes, sepsis, organ failure, and even death. It is suggested that about 1 in 5 infected people will experience no symptoms, although this number is highly variable depending on the population studied.

It is important to differentiate between asymptomatic and pre-symptomatic infections. Someone who is asymptomatic never develops symptoms, from the time they acquire the virus to the time the infection has fully cleared. Pre-symptomatic refers to someone who will eventually develop symptoms (it generally takes 7-13 days after the initial exposure to SARS-CoV-2 to develop symptoms).

It should be noted that even in the absence of symptoms, people can still transmit the virus and can act as a ‘silent driver’ of the pandemic.

The name coronavirus is derived from the Latin corona, meaning “crown.” This refers to the characteristic “crown” shape of the virus’ protein spikes.

This viral family has several members that can infect humans: four are potential causes of the common cold, while the others, SARS-CoV, MERS-CoV and SARS-CoV-2, have triggered dangerous epidemics. SARS-CoV-2 is a close relative to SARS-CoV, which was responsible for the severe acute respiratory syndrome (SARS) epidemic of 2002–2003, which infected over 8,000 people worldwide.

The morphology (shape) of coronavirus is depicted here with spike proteins (red) that form a corona (crown) around the virus. Additional proteins shown include envelope (yellow) and membrane (orange) proteins. Photo Credit: Alissa Eckert, MSMI, Dan Higgins, MAMS.

SARS-CoV-2 variants occur when there are changes or “mutations” in the original virus’ genetic code. These changes occur naturally over time as a by-product of replication.

For example, the B.1.1.7 variant was first identified in the United Kingdom where the mutation occurred on the receptor binding domain (RBD) of the spike protein at protein 501, and the amino acid asparagine (N) was replaced with tyrosine (Y).
Other variants have been identified, including the B.1.351 lineage that originated in South Africa and the P.1 lineage that originated in Brazil and Japan.

The SARS-CoV-2 variants are of concern because they appear to spread much faster and may impact the effectiveness of vaccines and therapeutics (medicines to help cure and soothe COVID-19 patients).

Figure 1.1. Rapidly spreading variants are being observed globally. Some mutations confer potential selective advantages to the virus, such as increased transmissibility or immune evasion. Photo Credit: Mariana Bego.

Figure 1.2. Rapidly spreading variants are being observed globally. Some mutations confer potential selective advantages to the virus, such as increased transmissibility or immune evasion. Photo credit: Mariana Bego.

Figure 1.3. When a person is infected with the virus such as SARS-CoV-2, the virus replicates many times in the host (humans). These viruses can be passed on from person to person through respiratory droplets (sneezing and coughing). With rapid virus replication and immune pressure to control the virus, this can cause the virus to mutate, generating a new variant. If the mutation found in the variant confers it some advantage, it will spread better in the population. Photo credit: Mariana Bego.

SARS-CoV-2 is the virus that causes the disease known as COVID-19.
Researchers are currently investigating this question. Research suggests prior coronavirus infections may result in the development of antibodies that fight against SARS-CoV-2, but these antibodies may not be strong enough to prevent COVID-19 infection.
Like with seasonal coronaviruses that cause the common cold, recovery from an initial infection gives a degree of immunity and protection towards re-infection. However, some patients who have recovered from COVID-19 have caught the virus for a second time.
COVID-19 causes diverse degrees of illness, ranging from asymptomatic infection (no symptoms) to mild symptoms, to severe pneumonia, strokes, sepsis, organ failure, and even death. It is suggested that about 1 in 5 infected people will experience no symptoms, although this number is highly variable depending on the population studied.

It is important to differentiate between asymptomatic and pre-symptomatic infections. Someone who is asymptomatic never develops symptoms, from the time they acquire the virus to the time the infection has fully cleared. Pre-symptomatic refers to someone who will eventually develop symptoms (it generally takes 7-13 days after the initial exposure to SARS-CoV-2 to develop symptoms).

It should be noted that even in the absence of symptoms, people can still transmit the virus and can act as a ‘silent driver’ of the pandemic.

SARS-CoV-2 Testing and Antibodies

Figure 2.1. The viral test involves a nose or throat swab and it detects the presence of the genetic material of the virus, telling you if you have an active infection. The antibody test involves a blood sample and it detects the antibodies created by your body to fight the virus. This tells you if you were infected in the past. Photo Credit: Mariana Bego.

A viral test, also known as diagnostic test, can tell you if you have an active COVID-19 infection which would require you to take steps to quarantine yourself to contain it.

The test is often performed with samples obtained from a throat or nose swab, as these areas are most likely to have enough virus to be detected. If you test positive, that means you have an active infection. Once the infection is resolved, the test would yield a negative result.

More specifically, the test itself looks for the presence of viral genetic material, called RNA, which resides inside living SARS-CoV-2, the virus that causes COVID-19.

Obtaining a negative result from a throat or nose swab test (viral test) does not imply that a person has never had COVID-19. It just means that the virus is no longer present or that there is so little of it left that it cannot be detected by the test.

A viral test can tell you if you are currently infected with SARS-CoV-2, while an antibody test can tell you if you have had an infection in the recent past.

Serology tests are used to determine is a person has previously been infected with SARS-CoV-2, the virus that causes COVID-19. Clinicians and researchers refer to them as serology tests, but often commercial laboratories will call them antibody tests. These tests look for the presence of antibodies, which are specific proteins made in response to infections. Antibody tests are particularly helpful in detecting previous infections in those who may have had few or no symptoms.

When our bodies detect the presence of a foreign or ‘never before seen’ protein, like a viral protein, we make antibodies. These antibodies are able to recognize and latch on to (or bind to) this foreign protein (called an antigen) in order to remove it from our bodies. This process is part of a healthy immune response targeting the foreign invader.

Antibodies can be detected in the blood of people who have been recently infected and, in many cases, long after the infection has been resolved. Another name for antibodies is immunoglobulins, shortened to Ig, and they come in a variety of flavours: IgA, IgM, IgG, IgE and IgD. Of these, IgM is the first to be made in response to a foreign protein and it can be found in blood for a short time after exposure to the foreign invaders (pathogens). IgG antibodies appear a little later in blood but can be detected for a longer period of time.

Antibodies bind strongly to the protein (or antigen) that they were made to recognize. This binding is highly specific, meaning they cannot bind to just any protein – only their target. The strength and specificity of their binding is the basis for many of their important roles: they can alert several branches of the immune system of an ongoing infection, and they can mark foreign proteins (and consequently the virus attached to them) to be ingested by immune cells and destroyed.

A unique type of antibody called a neutralizing antibody, will recognize proteins of the virus and prevent them from binding to the cell receptor, thereby blocking the virus’ entry into human cells. For SARS-CoV-2, this protein is the Spike (S).

Of the many proteins encoded by the virus, the Spike (S), which coats the outer layer of the virus, and the nucleocapsid (N), which wraps and protects the virus’ genomic component, are the most abundant. These proteins are often targeted by the immune system and are often recognized by antibodies. Antibodies recognizing the spike protein are dubbed anti-Spike IgG or (anti-S IgG, a-S IgG for short). Likewise, antibodies recognizing the nucleocapsid are named anti-Nucleocapsid IgG (anti-N or a-N for short).
Spike (S) proteins make up the outer layer of the virus. They are what give the virions (the viral infectious particles) the appearance of having a crown. Spike proteins are responsible for binding to the cellular receptor, an event required for the virus to enter into the human cell.

Figure 2.2. SARS-CoV-2 has the Spike (S) proteins that cover the outer membrane surface. These S proteins bind to a receptor called the angiotensin converting enzyme 2 (ACE2). The nucleocapsid protein forms complexes with the genomic RNA and is involved in viral replication. Photo Credit: Mariana Bego.

The CITF’s Immune Testing Working Party aims to enable accurate, quality assured, efficient, scalable, and safe immunity testing for SARS-CoV-2 across Canada. Given the novel status of SARS-CoV-2, all immune tests – whether based on blood draws from veins, pin pricks for blood spots, saliva samples, or others – require validation for accuracy. A test’s accuracy depends on its sensitivity and specificity, and the interpretation of a test is also dependent on the timing of testing in relation to an individual’s infection. Defining the duration of antibody responses will guide testing strategies and help understand the technology’s limitations.
A viral test, also known as diagnostic test, can tell you if you have an active COVID-19 infection which would require you to take steps to quarantine yourself to contain it.

The test is often performed with samples obtained from a throat or nose swab, as these areas are most likely to have enough virus to be detected. If you test positive, that means you have an active infection. Once the infection is resolved, the test would yield a negative result.

More specifically, the test itself looks for the presence of viral genetic material, called RNA, which resides inside living SARS-CoV-2, the virus that causes COVID-19.

Figure 2.1. The viral test involves a nose or throat swab and it detects the presence of the genetic material of the virus, telling you if you have an active infection. The antibody test involves a blood sample and it detects the antibodies created by your body to fight the virus. This tells you if you were infected in the past. Photo Credit: Mariana Bego.

Obtaining a negative result from a throat or nose swab test (viral test) does not imply that a person has never had COVID-19. It just means that the virus is no longer present or that there is so little of it left that it cannot be detected by the test.

A viral test can tell you if you are currently infected with SARS-CoV-2, while an antibody test can tell you if you have had an infection in the recent past.

Serology tests are used to determine is a person has previously been infected with SARS-CoV-2, the virus that causes COVID-19. Clinicians and researchers refer to them as serology tests, but often commercial laboratories will call them antibody tests. These tests look for the presence of antibodies, which are specific proteins made in response to infections. Antibody tests are particularly helpful in detecting previous infections in those who may have had few or no symptoms.

When our bodies detect the presence of a foreign or ‘never before seen’ protein, like a viral protein, we make antibodies. These antibodies are able to recognize and latch on to (or bind to) this foreign protein (called an antigen) in order to remove it from our bodies. This process is part of a healthy immune response targeting the foreign invader.

Antibodies can be detected in the blood of people who have been recently infected and, in many cases, long after the infection has been resolved. Another name for antibodies is immunoglobulins, shortened to Ig, and they come in a variety of flavours: IgA, IgM, IgG, IgE and IgD. Of these, IgM is the first to be made in response to a foreign protein and it can be found in blood for a short time after exposure to the foreign invaders (pathogens). IgG antibodies appear a little later in blood but can be detected for a longer period of time.

Antibodies bind strongly to the protein (or antigen) that they were made to recognize. This binding is highly specific, meaning they cannot bind to just any protein – only their target. The strength and specificity of their binding is the basis for many of their important roles: they can alert several branches of the immune system of an ongoing infection, and they can mark foreign proteins (and consequently the virus attached to them) to be ingested by immune cells and destroyed.

A unique type of antibody called a neutralizing antibody, will recognize proteins of the virus and prevent them from binding to the cell receptor, thereby blocking the virus’ entry into human cells. For SARS-CoV-2, this protein is the Spike (S).

Of the many proteins encoded by the virus, the Spike (S), which coats the outer layer of the virus, and the nucleocapsid (N), which wraps and protects the virus’ genomic component, are the most abundant. These proteins are often targeted by the immune system and are often recognized by antibodies. Antibodies recognizing the spike protein are dubbed anti-Spike IgG or (anti-S IgG, a-S IgG for short). Likewise, antibodies recognizing the nucleocapsid are named anti-Nucleocapsid IgG (anti-N or a-N for short).
Spike (S) proteins make up the outer layer of the virus. They are what give the virions (the viral infectious particles) the appearance of having a crown. Spike proteins are responsible for binding to the cellular receptor, an event required for the virus to enter into the human cell.

Figure 2.2. SARS-CoV-2 has the Spike (S) proteins that cover the outer membrane surface. These S proteins bind to a receptor called the angiotensin converting enzyme 2 (ACE2). The nucleocapsid protein forms complexes with the genomic RNA and is involved in viral replication. Photo Credit: Mariana Bego.

The CITF’s Immune Testing Working Party aims to enable accurate, quality assured, efficient, scalable, and safe immunity testing for SARS-CoV-2 across Canada. Given the novel status of SARS-CoV-2, all immune tests – whether based on blood draws from veins, pin pricks for blood spots, saliva samples, or others – require validation for accuracy. A test’s accuracy depends on its sensitivity and specificity, and the interpretation of a test is also dependent on the timing of testing in relation to an individual’s infection. Defining the duration of antibody responses will guide testing strategies and help understand the technology’s limitations.

Immunity

Figure 3.1. When an individual is infected with SARS-CoV-2, the innate immune response is initiated and characterized by dendritic cell (DC) activation. This is followed by an adaptive immune response where T and B cells are activated. T cells can perform many different functions, while B cells differentiate into plasma cells to produce antibodies. Both types of cells establish memory populations to prevent against re-infection. Photo Credit: Mariana Bego.

Immunity – a full defence against a virus or disease – is not offered by one element alone. There are several factors at play within immunity. Cell-mediated immunity (CMI) is the protective immune response generated by immune factors other than antibodies. This includes protection mediated by T lymphocytes (T cells), other white blood cells such as macrophages, and the soluble molecules (cytokines) which are produced by these immune cells.
In addition to cell-mediated immunity, antibody-mediated immunity is also a critical arm of the protective immune response. Antibody-mediated immunity is also referred to as humoral immunity and involves macromolecules found in fluids including antibodies produced by B cells and other blood proteins that are involved in fighting off pathogens. Antibodies have several functions, one of which is blocking a virus from entering and infecting a cell. This is known as “neutralization”.
T cells are an important part of the immune response mounted by our body in response to pathogens such as SARS-CoV-2. There are several subtypes of T cells that respond to different types of pathogens, and they play a critical role in shaping the overall immune response. T cells have proteins on their surface that can detect and kill SARS-CoV-2-infected cells. They can also release a wide range of small soluble molecules (cytokines) that can recruit other immune cells to help clear the infection. T cells also influence the antibody response against SARS-CoV-2 by shaping the type of antibodies generated against the virus. Finally, once the infection is cleared, T cells establish themselves as a small memory population that is pre-primed and ready to react to any future re-exposure to SARS-CoV-2, thus protecting against any subsequent infection that may occur.
Once an individual has recovered from SARS-CoV-2 infection, their immune system remains primed for subsequent re-exposure to the virus. This is enabled by immune cells that have previously recognized and resolved the initial SARS-CoV-2 infection. These immune cells, specifically for SARS-CoV-2, establish long-living memory populations which are ready to respond to re-exposure to the same virus.

While early studies have indicated that antibody levels themselves may drop soon after the initial infection ends, both B cells (cells that produce antibodies) and T cells (cells that enable cell-mediated immunity) establish memory populations and form a protective response to prevent against subsequent re-infection. Currently, it is unknown how long the protective response can remain, but CITF is funding several studies looking into this. So far, researchers have shown that COVID-19 respondents develop memory responses that have lasted at least 3-8 months post-infection.

People infected with SARS-CoV-2 develop an immune response against the virus. This process is facilitated by immune cells known as B and T cells, which are responsible for generating both antibody-mediated and cell-mediated immunity, respectively. Upon clearance of the initial infection, these cells establish a long-lasting memory population that remains primed and ready to resolve subsequent infection by the same virus.

That said, depending on the individual and the severity of the primary infection, the level of these protective antibodies may drop progressively over time. While scientists (including some funded by the CITF) are still trying to understand the longevity of the memory response primed against SARS-CoV-2, re-exposure to the same virus can potentially help remind the immune system and boost these specific antibody- and cell-mediated responses. Consequently, this may help restore antibody levels to better protect against subsequent re-infections.

CITF-funded researchers are involved in characterizing SARS-CoV-2 humoral and cell-mediated responses. These include antibody titers, neutralization, T cell exhaustion, immune senescence, longevity and durability of the immune response to SARS-CoV-2. Researchers are also involved in studying conditions and immune factors that are associated with reinfections and the correlates of protection from re-infection with SARS-CoV-2.

Herd immunity is when a large proportion of the population is immune to a specific disease such as COVID-19, reducing the spread of the disease from person to person. Although not every individual is immune to the virus or bacteria, the majority of those immune protects the rest of the individuals (including newborns or immunocompromised individuals who cannot be vaccinated) from getting infected.

Herd immunity can be achieved by having enough individuals infected with the virus or it can be achieved with vaccinations. Vaccinations are the ideal approach for achieving herd immunity and it was reported by some studies that at least 70-85% of the population would need to be immune to achieve herd immunity. Herd immunity depends on the reproduction number or R0, which tells us the average number of people that a single person with the virus can infect. A higher R0 indicates more people need to be immune to reach herd immunity.

Figure 3.2. Herd immunity is achieved when there is a large proportion of individuals that are immune to SARS-CoV-2 that would reduce the risk of the remaining individuals from getting infected. Photo Credit: Mariana Bego.

Correlates of protection to a virus or an infectious pathogen are measurable signs that a person (or other potential host) is immune, in the sense of being protected against becoming infected and/or developing disease. For many viruses, antibodies serve as a correlate of immunity, but they are not the only element to consider when determining whether a person is completely immune. Unfortunately, the correlates of protection against SARS-CoV-2 are still not completely understood.

CITF-funded researchers are interested in defining the markers that are associated with protective immunity against SARS-CoV-2 infection. Factors under consideration include presence and minimum thresholds of binding antibodies and neutralizing antibodies against the SARS-CoV-2 spike and nucleocapsid proteins. T and B cells are also being studied to determine their role in protection as they are shown to last longer than antibodies. Researchers would like to determine if 1) If these are good markers and 2) how much of these markers are needed to confer protection.

Immunity – a full defence against a virus or disease – is not offered by one element alone. There are several factors at play within immunity. Cell-mediated immunity (CMI) is the protective immune response generated by immune factors other than antibodies. This includes protection mediated by T lymphocytes (T cells), other white blood cells such as macrophages, and the soluble molecules (cytokines) which are produced by these immune cells.

Figure 3.1. When an individual is infected with SARS-CoV-2, the innate immune response is initiated and characterized by dendritic cell (DC) activation. This is followed by an adaptive immune response where T and B cells are activated. T cells can perform many different functions, while B cells differentiate into plasma cells to produce antibodies. Both types of cells establish memory populations to prevent against re-infection. Photo Credit: Mariana Bego.

In addition to cell-mediated immunity, antibody-mediated immunity is also a critical arm of the protective immune response. Antibody-mediated immunity is also referred to as humoral immunity and involves macromolecules found in fluids including antibodies produced by B cells and other blood proteins that are involved in fighting off pathogens. Antibodies have several functions, one of which is blocking a virus from entering and infecting a cell. This is known as “neutralization”.
T cells are an important part of the immune response mounted by our body in response to pathogens such as SARS-CoV-2. There are several subtypes of T cells that respond to different types of pathogens, and they play a critical role in shaping the overall immune response. T cells have proteins on their surface that can detect and kill SARS-CoV-2-infected cells. They can also release a wide range of small soluble molecules (cytokines) that can recruit other immune cells to help clear the infection. T cells also influence the antibody response against SARS-CoV-2 by shaping the type of antibodies generated against the virus. Finally, once the infection is cleared, T cells establish themselves as a small memory population that is pre-primed and ready to react to any future re-exposure to SARS-CoV-2, thus protecting against any subsequent infection that may occur.
Once an individual has recovered from SARS-CoV-2 infection, their immune system remains primed for subsequent re-exposure to the virus. This is enabled by immune cells that have previously recognized and resolved the initial SARS-CoV-2 infection. These immune cells, specifically for SARS-CoV-2, establish long-living memory populations which are ready to respond to re-exposure to the same virus.

While early studies have indicated that antibody levels themselves may drop soon after the initial infection ends, both B cells (cells that produce antibodies) and T cells (cells that enable cell-mediated immunity) establish memory populations and form a protective response to prevent against subsequent re-infection. Currently, it is unknown how long the protective response can remain, but CITF is funding several studies looking into this. So far, researchers have shown that COVID-19 respondents develop memory responses that have lasted at least 3-8 months post-infection.

People infected with SARS-CoV-2 develop an immune response against the virus. This process is facilitated by immune cells known as B and T cells, which are responsible for generating both antibody-mediated and cell-mediated immunity, respectively. Upon clearance of the initial infection, these cells establish a long-lasting memory population that remains primed and ready to resolve subsequent infection by the same virus.

That said, depending on the individual and the severity of the primary infection, the level of these protective antibodies may drop progressively over time. While scientists (including some funded by the CITF) are still trying to understand the longevity of the memory response primed against SARS-CoV-2, re-exposure to the same virus can potentially help remind the immune system and boost these specific antibody- and cell-mediated responses. Consequently, this may help restore antibody levels to better protect against subsequent re-infections.

CITF-funded researchers are involved in characterizing SARS-CoV-2 humoral and cell-mediated responses. These include antibody titers, neutralization, T cell exhaustion, immune senescence, longevity and durability of the immune response to SARS-CoV-2. Researchers are also involved in studying conditions and immune factors that are associated with reinfections and the correlates of protection from re-infection with SARS-CoV-2.

Herd immunity is when a large proportion of the population is immune to a specific disease such as COVID-19, reducing the spread of the disease from person to person. Although not every individual is immune to the virus or bacteria, the majority of those immune protects the rest of the individuals (including newborns or immunocompromised individuals who cannot be vaccinated) from getting infected.

Herd immunity can be achieved by having enough individuals infected with the virus or it can be achieved with vaccinations. Vaccinations are the ideal approach for achieving herd immunity and it was reported by some studies that at least 70-85% of the population would need to be immune to achieve herd immunity. Herd immunity depends on the reproduction number or R0, which tells us the average number of people that a single person with the virus can infect. A higher R0 indicates more people need to be immune to reach herd immunity.

Figure 3.2. Herd immunity is achieved when there is a large proportion of individuals that are immune to SARS-CoV-2 that would reduce the risk of the remaining individuals from getting infected. Photo Credit: Mariana Bego.

Correlates of protection to a virus or an infectious pathogen are measurable signs that a person (or other potential host) is immune, in the sense of being protected against becoming infected and/or developing disease. For many viruses, antibodies serve as a correlate of immunity, but they are not the only element to consider when determining whether a person is completely immune. Unfortunately, the correlates of protection against SARS-CoV-2 are still not completely understood.

CITF-funded researchers are interested in defining the markers that are associated with protective immunity against SARS-CoV-2 infection. Factors under consideration include presence and minimum thresholds of binding antibodies and neutralizing antibodies against the SARS-CoV-2 spike and nucleocapsid proteins. T and B cells are also being studied to determine their role in protection as they are shown to last longer than antibodies. Researchers would like to determine if 1) If these are good markers and 2) how much of these markers are needed to confer protection.

Serosurveillance and other population-based studies

Figure 4.1. Using a spring-loaded lancet provided in the test kit, drops of blood from a fingerprick are placed onto the DBS filter paper card. The DBS is then sealed, packaged, labelled and shipped to an analytical lab, where it is processed and analyzed for the presence of SARS-CoV-2 antibodies. A positive result would be indicative of a past infection. Photo Credit: Kristin Davis.

Health surveillance is common in public health. It is a way of observing and monitoring the health and wellness of large groups of people. Serosurveillance monitors and estimates antibody levels in blood samples from certain groups of people against infectious agents, such as SARS-CoV-2, the virus that causes COVID-19. The goal is to measure how many people have been exposed to SARS-CoV-2 and have subsequently developed antibodies. This will help researchers estimate population immunity resulting from a past infection or vaccination. When it’s known how many people have antibodies to ward off potential infection, or at least serious forms of infection, public health officials can more confidently inform and protect people.

To understand population immunity to the SARS-CoV-2 virus, blood samples from thousands of Canadians are currently being tested to check levels of antibodies directed against SARS-CoV-2 proteins.

Seroprevalence is the number (or percentage) of people in a population who test positive for a specific virus or infectious agent, based on blood tests. If the seroprevalence is 1%, for example, this suggests that 1% of the population studied has antibodies to the virus or infectious agent and therefore could have some form of resistance to it.

Sometimes referred to as field studies, population-based studies aim to answer research questions for defined populations, based on a sample of that population. These populations of interest can be large, like the entire population of a city, or they can be defined by a single characteristic shared by a number of people, like children between the ages of 3 and 5.

These studies are traditionally described as studies that involve a defined “general population,” as opposed to a hospital-based or occupation-based population.

To extrapolate statistics from population-based studies, several minimum requirements need to be met:

  1. The sample of individuals needs to be big enough, randomly selected, and representative of the general population;
  2. The measurements need to be standardized;
  3. The tests used need to have adequate sensitivity and specificity.

Population-based seroprevalence surveys of COVID-19 help us to do things like estimate how infectious the virus is and its fatality rate. They can tell us, for example, how much transmission is due to asymptomatic and mild infections. They can also help us identify exposed and susceptible populations.

These types of studies are well suited to inform evidence-based policy decisions.

CITF-funded researchers are involved in large pan-provincial projects estimating seroprevalence by region and province. They are also involved in estimating seroprevalence among populations of interest such as school-aged children, long-term care facilities, health care workers and geographical hotspots, among others. You can see a complete list of our funded studies here.

Core data elements are a standardized list of questions developed by CITF experts that must be integrated into surveys done by CITF-funded groups studying immunity. These core data elements aim to encourage the many CITF-funded research groups to acquire and record survey data in a standardized manner. The goal is for the CITF to be able to directly compare results from different COVID-19 studies and initiatives across Canada.

Specifically, the core data elements include questions and responses related to COVID-19 status, COVID-19 symptoms, quality of housing, risk factors, risk acquisitions, vaccines and health behaviour changes related to the virus.

A DBS, or dried blood spot kit, is an easy-to-use way to take a blood sample that people can do at home. It’s a great alternative to having blood drawn in a clinic, as people don’t have to leave home to do it. The participant is asked to follow a step-by-step process which involves them pricking their finger and depositing several blood drops onto a card which is then mailed back to a laboratory for analysis. Please see a video made by one of our funded studies here.

Currently, these kits are being used by a number of seroprevalence studies supported by the CITF in order to collect blood for antibody testing. Scientists use the collected blood spots to determine the presence of SARS-CoV-2 antibodies in a surveyed population.

As vaccines become available, serosurveillance can help us determine priority groups for vaccination by identifying populations that remain vulnerable to infection. Seroprevalence studies can also help us monitor the effectiveness of the existing vaccination programs.

SARS-CoV-2 is a relatively new virus so there are many questions that still need to be answered. For example, at this stage in the pandemic, we still don’t know for certain how long antibodies (from a COVID-19 infection or a vaccine) remain in the body. By continuing to gather as much information as possible about the virus, we improve our ability to mount a comprehensive and well-informed response against it.

Vaccine surveillance studies look at vaccine effectiveness (how good are vaccines at preventing severe disease, new infections, and transmission?) and vaccine safety (identifying and quantifying the vaccine’s adverse effects). An adverse effect is an undesired harmful effect resulting from a medication or other intervention.

Vaccine surveillance also looks more precisely at the immune response generated by the vaccine (how successful is the vaccine at developing a protective immune response? What are the details of the vaccine-induced immune response? How long can these “markers of protection” be detected? How long will the vaccine work?).

Vaccine surveillance covers vaccine confidence which explores the driving factors behind any concerns people may have about getting vaccinated (aka. vaccine hesitancy).

Natural immunity is better termed “infection-acquired immunity”. It means the person has some form of defence against the virus due to an infection or exposure – not thanks to a vaccine. Vaccine-induced immunity refers to the body’s defence mechanism against a virus thanks to a vaccine.

Currently, there is no consensus on how long either type of immunity lasts.

Health surveillance is common in public health. It is a way of observing and monitoring the health and wellness of large groups of people. Serosurveillance monitors and estimates antibody levels in blood samples from certain groups of people against infectious agents, such as SARS-CoV-2, the virus that causes COVID-19. The goal is to measure how many people have been exposed to SARS-CoV-2 and have subsequently developed antibodies. This will help researchers estimate population immunity resulting from a past infection or vaccination. When it’s known how many people have antibodies to ward off potential infection, or at least serious forms of infection, public health officials can more confidently inform and protect people.

To understand population immunity to the SARS-CoV-2 virus, blood samples from thousands of Canadians are currently being tested to check levels of antibodies directed against SARS-CoV-2 proteins.

Seroprevalence is the number (or percentage) of people in a population who test positive for a specific virus or infectious agent, based on blood tests. If the seroprevalence is 1%, for example, this suggests that 1% of the population studied has antibodies to the virus or infectious agent and therefore could have some form of resistance to it.

Sometimes referred to as field studies, population-based studies aim to answer research questions for defined populations, based on a sample of that population. These populations of interest can be large, like the entire population of a city, or they can be defined by a single characteristic shared by a number of people, like children between the ages of 3 and 5.

These studies are traditionally described as studies that involve a defined “general population,” as opposed to a hospital-based or occupation-based population.

To extrapolate statistics from population-based studies, several minimum requirements need to be met:

  1. The sample of individuals needs to be big enough, randomly selected, and representative of the general population;
  2. The measurements need to be standardized;
  3. The tests used need to have adequate sensitivity and specificity.

Population-based seroprevalence surveys of COVID-19 help us to do things like estimate how infectious the virus is and its fatality rate. They can tell us, for example, how much transmission is due to asymptomatic and mild infections. They can also help us identify exposed and susceptible populations.

These types of studies are well suited to inform evidence-based policy decisions.

CITF-funded researchers are involved in large pan-provincial projects estimating seroprevalence by region and province. They are also involved in estimating seroprevalence among populations of interest such as school-aged children, long-term care facilities, health care workers and geographical hotspots, among others. You can see a complete list of our funded studies here.

Core data elements are a standardized list of questions developed by CITF experts that must be integrated into surveys done by CITF-funded groups studying immunity. These core data elements aim to encourage the many CITF-funded research groups to acquire and record survey data in a standardized manner. The goal is for the CITF to be able to directly compare results from different COVID-19 studies and initiatives across Canada.

Specifically, the core data elements include questions and responses related to COVID-19 status, COVID-19 symptoms, quality of housing, risk factors, risk acquisitions, vaccines and health behaviour changes related to the virus.

A DBS, or dried blood spot kit, is an easy-to-use way to take a blood sample that people can do at home. It’s a great alternative to having blood drawn in a clinic, as people don’t have to leave home to do it. The participant is asked to follow a step-by-step process which involves them pricking their finger and depositing several blood drops onto a card which is then mailed back to a laboratory for analysis. Please see a video made by one of our funded studies here.

Currently, these kits are being used by a number of seroprevalence studies supported by the CITF in order to collect blood for antibody testing. Scientists use the collected blood spots to determine the presence of SARS-CoV-2 antibodies in a surveyed population.

Figure 4.1. Using a spring-loaded lancet provided in the test kit, drops of blood from a fingerprick are placed onto the DBS filter paper card. The DBS is then sealed, packaged, labelled and shipped to an analytical lab, where it is processed and analyzed for the presence of SARS-CoV-2 antibodies. A positive result would be indicative of a past infection. Photo Credit: Kristin Davis.

As vaccines become available, serosurveillance can help us determine priority groups for vaccination by identifying populations that remain vulnerable to infection. Seroprevalence studies can also help us monitor the effectiveness of the existing vaccination programs.

SARS-CoV-2 is a relatively new virus so there are many questions that still need to be answered. For example, at this stage in the pandemic, we still don’t know for certain how long antibodies (from a COVID-19 infection or a vaccine) remain in the body. By continuing to gather as much information as possible about the virus, we improve our ability to mount a comprehensive and well-informed response against it.

Vaccine surveillance studies look at vaccine effectiveness (how good are vaccines at preventing severe disease, new infections, and transmission?) and vaccine safety (identifying and quantifying the vaccine’s adverse effects). An adverse effect is an undesired harmful effect resulting from a medication or other intervention.

Vaccine surveillance also looks more precisely at the immune response generated by the vaccine (how successful is the vaccine at developing a protective immune response? What are the details of the vaccine-induced immune response? How long can these “markers of protection” be detected? How long will the vaccine work?).

Vaccine surveillance covers vaccine confidence which explores the driving factors behind any concerns people may have about getting vaccinated (aka. vaccine hesitancy).

Natural immunity is better termed “infection-acquired immunity”. It means the person has some form of defence against the virus due to an infection or exposure – not thanks to a vaccine. Vaccine-induced immunity refers to the body’s defence mechanism against a virus thanks to a vaccine.

Currently, there is no consensus on how long either type of immunity lasts.

Vaccines

Figure 5.1. The COVID-19 mRNA vaccine contains instructions (mRNA) to make a lot of SARS-CoV-2 Spike proteins. The release of this Spike protein outside of the host cell triggers an immune response and the host makes antibodies, B cells, and T cells against the virus, similar to what happens in natural infection. Photo Credit: Mariana Bego.

COVID-19 vaccines trigger our bodies to develop immunity against SARS-CoV-2 without us having to get the disease first. There are currently four main types of COVID-19 vaccines: messenger RNA (mRNA) vaccines (such as Pfizer-BioNTech and Moderna), protein subunit vaccines, vector vaccines (such as Johnson & Johnson and AstraZeneca), and inactivated virus vaccines.

The mRNA vaccine is the newest type of vaccine that teaches our cells to make a copy of a protein unique to SARS-CoV-2 called the Spike protein. Our body recognizes these proteins as foreign and generates antibodies and build B and T cells to remember the virus so we can defeat it if we are infected in the future.

The protein subunit vaccines consist of harmless proteins of the SARS-CoV-2 virus, while vector vaccines contain a different harmless virus that enters our cells to produce the SARS-CoV-2 Spike protein. Lastly, the inactivated SARS-CoV-2 vaccine consists of the killed virus that no longer replicates. All types of vaccines have the same end goal: generate a supply of memory B and T cells to remember how to the fight the virus in the future. The levels and duration of immunity offered by these different vaccines, however, may vary.

Vaccines against SARS-CoV-2 have been developed to prime your body’s immune response to ensure that it fights against the virus, reducing the risk of you getting COVID-19. These vaccines are especially good at reducing the risk of severe COVID-19 symptoms. Studies do suggest that vaccinated individuals have reduced numbers of virus in the blood, which would in turn suppress transmission. To determine if vaccines do indeed prevent transmission, studies are currently underway to track close contacts of vaccinated individuals to determine if they are protected from infection. That said, given that there are individual variations in immune responses, a vaccinated individual can still transmit the virus for a period of time after infection. Therefore, it is extremely important that vaccinated individuals continue to follow public health guidelines including frequent hand washing, maintaining a safe distance from others, wearing a mask, and staying home if feeling unwell.

If you had COVID-19 previously, you should still get vaccinated because the level of immunity from natural infection is not entirely clear. The vaccine also will provide longer-term protection as it has been optimally designed to generate an effective immune response. There is no harm in getting a vaccine to boost your immune response to SARS-CoV-2.

Vaccine effectiveness is measured by the impact of vaccination on COVID-19-related hospitalizations, mortality, effects of COVID-19 vaccination on asymptomatic infection and transmission, and how groups of different ages, and overall health status respond to the vaccine. Some of the studies supported by the Vaccine Surveillance Reference Group (VSRG) include assessing effectiveness with different combinations of vaccines, vaccinations in pregnant women and children, and vaccine effectiveness for prevention of serious outcomes among hospitalized adults.

The Vaccine Surveillance Reference Group (VSRG) is involved in supporting research studies which evaluate vaccine safety. Vaccine safety is evaluated by tracking adverse events including an association with anaphylaxis and other allergic events, Guillain-Barré syndrome, Bell’s palsy, and vaccine-associated enhanced disease. Some studies supported by VSRG are documenting severe health events including local injection site reactions, systemic symptoms (fever, fatigue, myalgia), respiratory symptoms suggestive of cold, flu, COVID-19, and gastrointestinal symptoms (nausea, vomiting, diarrhea or stomach pain). The populations studied overlap with those studies that are measuring effectiveness and include pregnant women, children, and hospitalized adults.

The current vaccines approved for use were tested before the new variants emerged so there is insufficient evidence to determine how effectively the vaccines will work against them.

Preliminary studies show that individuals vaccinated with the Pfizer-BioNTech’s mRNA vaccine can neutralize both the variants originating from the UK and South Africa.  Another study has shown that there was a reduction in the capability of Moderna’s mRNA-1273 to ward off the variant originating from South Africa. Lastly, Novavax announced that their vaccine had a vaccine efficacy of 89.3% in a UK population where there was high prevalence of the variant originating from the UK, suggesting that it is effective against this variant. Altogether, these studies suggest the importance of continuous monitoring of the variants as this could indicate a need for a vaccine strain change.

In an ideal world, there would be a sufficient supply of vaccine to administer to the entire population using approved clinical trial dosing intervals. Due to vaccine supply shortages, countries have been faced with the difficult decision to delay the second dose to maximize the number of people receiving their first dose. Based on clinical trials, the manufacturers of the SARS-CoV-2 vaccines recommend two doses at specific intervals to achieve optimal efficacy. It is possible however that a longer interval between the vaccine doses could improve immunity as has been shown for the Oxford-AstraZeneca vaccine.

Canada’s National Advisory Committee on Immunization (NACI) has recommended that in the context of limited COVID-19 vaccine supply, individuals can receive their second dose up to four months after receiving their first dose. This is based on data from Quebec, British Columbia, Israel, the United Kingdom and the United States supporting 70-80% effectiveness from a single dose of mRNA vaccines for up to two months. Modelling by the Public Health Agency of Canada also suggested intervals could be extended up to six months between doses. However, there is insufficient long-term follow-up in clinical trials to understand the actual duration of protection.

Most vaccines are given as two doses to offer the maximum benefit of protection against SARS-CoV-2. The Pfizer-BioNTech, Moderna, and Oxford-AstraZeneca are all given as a two-dose series, while the Johnson & Johnson vaccine is a single-dose shot which has been shown to be effective in preventing symptomatic COVID-19 disease beginning two weeks after vaccination in clinical trials.

The first dose acts to prime immunological memory, while the second dose acts as a boost to extend protection over the longer term. This essentially means that more exposure time allows the body a chance to produce more antibodies and memory cells to fight off the virus. Protection offered by the first dose is lower than the efficacy achieved after the second dose. Peak levels of humoral and cellular responses are observed after this second dose.

COVID-19 vaccines trigger our bodies to develop immunity against SARS-CoV-2 without us having to get the disease first. There are currently four main types of COVID-19 vaccines: messenger RNA (mRNA) vaccines (such as Pfizer-BioNTech and Moderna), protein subunit vaccines, vector vaccines (such as Johnson & Johnson and AstraZeneca), and inactivated virus vaccines.

The mRNA vaccine is the newest type of vaccine that teaches our cells to make a copy of a protein unique to SARS-CoV-2 called the Spike protein. Our body recognizes these proteins as foreign and generates antibodies and build B and T cells to remember the virus so we can defeat it if we are infected in the future.

The protein subunit vaccines consist of harmless proteins of the SARS-CoV-2 virus, while vector vaccines contain a different harmless virus that enters our cells to produce the SARS-CoV-2 Spike protein. Lastly, the inactivated SARS-CoV-2 vaccine consists of the killed virus that no longer replicates. All types of vaccines have the same end goal: generate a supply of memory B and T cells to remember how to the fight the virus in the future. The levels and duration of immunity offered by these different vaccines, however, may vary.

Figure 5.1. The COVID-19 mRNA vaccine contains instructions (mRNA) to make a lot of SARS-CoV-2 Spike proteins. The release of this Spike protein outside of the host cell triggers an immune response and the host makes antibodies, B cells, and T cells against the virus, similar to what happens in natural infection. Photo Credit: Mariana Bego.

Vaccines against SARS-CoV-2 have been developed to prime your body’s immune response to ensure that it fights against the virus, reducing the risk of you getting COVID-19. These vaccines are especially good at reducing the risk of severe COVID-19 symptoms. Studies do suggest that vaccinated individuals have reduced numbers of virus in the blood, which would in turn suppress transmission. To determine if vaccines do indeed prevent transmission, studies are currently underway to track close contacts of vaccinated individuals to determine if they are protected from infection. That said, given that there are individual variations in immune responses, a vaccinated individual can still transmit the virus for a period of time after infection. Therefore, it is extremely important that vaccinated individuals continue to follow public health guidelines including frequent hand washing, maintaining a safe distance from others, wearing a mask, and staying home if feeling unwell.

If you had COVID-19 previously, you should still get vaccinated because the level of immunity from natural infection is not entirely clear. The vaccine also will provide longer-term protection as it has been optimally designed to generate an effective immune response. There is no harm in getting a vaccine to boost your immune response to SARS-CoV-2.

Vaccine effectiveness is measured by the impact of vaccination on COVID-19-related hospitalizations, mortality, effects of COVID-19 vaccination on asymptomatic infection and transmission, and how groups of different ages, and overall health status respond to the vaccine. Some of the studies supported by the Vaccine Surveillance Reference Group (VSRG) include assessing effectiveness with different combinations of vaccines, vaccinations in pregnant women and children, and vaccine effectiveness for prevention of serious outcomes among hospitalized adults.

The Vaccine Surveillance Reference Group (VSRG) is involved in supporting research studies which evaluate vaccine safety. Vaccine safety is evaluated by tracking adverse events including an association with anaphylaxis and other allergic events, Guillain-Barré syndrome, Bell’s palsy, and vaccine-associated enhanced disease. Some studies supported by VSRG are documenting severe health events including local injection site reactions, systemic symptoms (fever, fatigue, myalgia), respiratory symptoms suggestive of cold, flu, COVID-19, and gastrointestinal symptoms (nausea, vomiting, diarrhea or stomach pain). The populations studied overlap with those studies that are measuring effectiveness and include pregnant women, children, and hospitalized adults.

The current vaccines approved for use were tested before the new variants emerged so there is insufficient evidence to determine how effectively the vaccines will work against them.

Preliminary studies show that individuals vaccinated with the Pfizer-BioNTech’s mRNA vaccine can neutralize both the variants originating from the UK and South Africa.  Another study has shown that there was a reduction in the capability of Moderna’s mRNA-1273 to ward off the variant originating from South Africa. Lastly, Novavax announced that their vaccine had a vaccine efficacy of 89.3% in a UK population where there was high prevalence of the variant originating from the UK, suggesting that it is effective against this variant. Altogether, these studies suggest the importance of continuous monitoring of the variants as this could indicate a need for a vaccine strain change.

In an ideal world, there would be a sufficient supply of vaccine to administer to the entire population using approved clinical trial dosing intervals. Due to vaccine supply shortages, countries have been faced with the difficult decision to delay the second dose to maximize the number of people receiving their first dose. Based on clinical trials, the manufacturers of the SARS-CoV-2 vaccines recommend two doses at specific intervals to achieve optimal efficacy. It is possible however that a longer interval between the vaccine doses could improve immunity as has been shown for the Oxford-AstraZeneca vaccine.

Canada’s National Advisory Committee on Immunization (NACI) has recommended that in the context of limited COVID-19 vaccine supply, individuals can receive their second dose up to four months after receiving their first dose. This is based on data from Quebec, British Columbia, Israel, the United Kingdom and the United States supporting 70-80% effectiveness from a single dose of mRNA vaccines for up to two months. Modelling by the Public Health Agency of Canada also suggested intervals could be extended up to six months between doses. However, there is insufficient long-term follow-up in clinical trials to understand the actual duration of protection.

Most vaccines are given as two doses to offer the maximum benefit of protection against SARS-CoV-2. The Pfizer-BioNTech, Moderna, and Oxford-AstraZeneca are all given as a two-dose series, while the Johnson & Johnson vaccine is a single-dose shot which has been shown to be effective in preventing symptomatic COVID-19 disease beginning two weeks after vaccination in clinical trials.

The first dose acts to prime immunological memory, while the second dose acts as a boost to extend protection over the longer term. This essentially means that more exposure time allows the body a chance to produce more antibodies and memory cells to fight off the virus. Protection offered by the first dose is lower than the efficacy achieved after the second dose. Peak levels of humoral and cellular responses are observed after this second dose.