This evidence synthesis has been compiled by members of the CITF Secretariat and does not necessarily represent the views of all CITF members.

By Mariana Bego

Several studies have recently evaluated the protection against reinfection with SARS-CoV-2, the virus that causes COVID-19. A recent article in The Lancet studied the situation in Denmark, where 70% of the entire population (or 4 million people) was tested for SARS-CoV-2 by PCR as part of the country’s nationwide free-of-charge testing strategy.

The authors from the University of Copenhagen retrieved data recorded in the Danish national COVID-19 surveillance database, to follow over half a million of these individuals from the first to the second wave of the SARS-CoV-2 pandemic and evaluate the rates of reinfection. During the first wave, only roughly 2% of the individuals tested positive for SARS-CoV-2 (approximately 12,000 positive results from 533,381 individuals tested). From the eligible 525,339 individuals who tested negative in the first wave, around 3% were positive in the second wave (approximately 17,000 positive results). Of the PCR-positive individuals from the first wave of the epidemic, only 72 (0.65%) got reinfected during the second wave. With these numbers, the authors calculated that protection against repeat infection to be around 80%.

But when the analysis was repeated while segregating subjects by age, they noted that protection for people who already had COVID-19 dropped to under 50% for those ages 65 and older. The authors hypothesize that this is the result of immune function diminishing with age. Finally, they recommended that based on their analysis, people over 65 should be vaccinated even if they were previously infected, as natural protection may not be sufficient to protect them from reinfection.

Masks and social distancing are still the best way to prevent reinfection as the risk of reinfection increases proportionally with the number of viral particles a person is exposed to. Experts continue to recommend that people who have had the disease, or have been vaccinated, take precautions to limit their exposure.

Read their article here.


A team of researchers from Cornell University wondered whether the quantity and quality of antibodies against SARS-CoV-2 was different among children, adolescents, young adults and older populations. Their results can be found in an article from last week’s JAMA Network journal. In this article, over 30,000 SARS-CoV-2 antibody test results from a single testing platform were used. Infants under 1 were not included, to limit the possibility of antibody transfer from mother to child.

In contrast to previous studies, the authors used samples from individuals recovering from COVID-19, limiting themselves to either asymptomatic or mildly ill non-hospitalized patients, which is more representative of the overall pediatric population of patients with COVID-19.

Samples from children (aged 1 to 10 years) and adults (aged 51 to 80 years) showed significantly higher SARS-CoV-2-specific antibody levels than the young adult group (ages 19 to 30). It remains unclear why patients aged 19 to 30 exhibited lower levels of SARS-CoV-2 IgG antibodies than children and older adults. The results of this study also indicate that the anti–SARS-CoV-2 immune response in younger children is more robust than that in adolescents and young adults, not only in magnitude but also regarding the functional capacity of antibodies to eliminate the virus. The authors suggest that the differences in clinical manifestations of COVID-19 between pediatric and adult patients could be partly due to age-related immune responses.

Read their article here.