This is a summary, written by members of the CITF Secretariat, of:
Tauzin A, Nayrac M, Benlarbi M, Gong SY, Gasser R, Beaudoin-Bussières G, Brassard N, Laumaea A, Vézina D, Prévost J, Anand SP, Bourassa C, Gendron-Lepage G, Medjahed H, Goyette G, Niessl J, Tastet O, Gokool L, Morrisseau C, Arlotto P, Stamatatos L, McGuire AT, Larochelle C, Uchil P, Lu M, Mothes W, De Serres G, Moreira S, Roger M, Richard J, Martel-Laferrière V, Duerr R, Tremblay C, Kaufmann DE, Finzi A. A single dose of the SARS-CoV-2 vaccine BNT162b2 elicits Fc-mediated antibody effector functions and T-cell responses. Cell Host and Microbe. 2021 Jun 4. doi: 10.1016/j.chom.2021.06.001.
The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.
Scientists from Université de Montréal, including Dr. Cecile Tremblay and CITF-funded researchers Drs. Daniel Kaufmann and Andrés Finzi, conducted a comprehensive study of the immune response against SARS-CoV-2, three weeks after a single dose of the Pfizer-BioNTech COVID-19 vaccine. They reported a robust response, especially in individuals with a history of COVID-19. Their study, published in Cell Host and Microbe, supports the rationale for spacing doses in order to initially partially vaccinate a higher number of individuals in the context of vaccine scarcity.
- In individuals without prior exposure to SARS-COV-2, antibodies showed weak neutralization capacity, but otherwise strong functional antibody responses were elicited.
- Sizeable cellular immune responses, mostly due to T helper cells, were also observed.
- Vaccination boosted the immune responses of individuals who had previously been infected.
The Pfizer-BioNTech COVID-19 vaccine uses messenger RNA (mRNA) technology to program cells to make spike proteins that resemble those of SARS-CoV-2. An effective vaccine is expected to induce a strong production of antibodies (humoral immune response) towards the spike protein and its receptor-binding domain (RBD), as well as prime (or educate) specific T cells (cellular immune response). Vaccine-induced cellular immune responses are important to sustain long-lived immunity as well as to encourage a rich production of antibodies. Both humoral and cellular responses were indeed observed after the dual dosage regime administered three weeks apart during the early trials done by the manufacturer. In light of vaccine scarcity however, many public health authorities are recommending the administration of doses more than three weeks apart.
The authors of this study evaluated the immune responses against SARS-CoV-2 three weeks after the first dose of vaccine. They compared immune markers in 24 individuals who had not previously been infected with SARS-CoV-2, and in 24 who had been infected around nine months earlier.
They observed low levels of neutralizing antibodies Antibodies that bind to the surface structures of a pathogen, preventing it from entering and infecting its host cells. in SARS-CoV-2 naïve individuals, i.e., those without prior exposure to SARS-COV-2, but excellent levels of antibodies recognizing the full Spike and the RBD. Vaccination in the SARS-CoV-2 naïve group elicited antibody levels comparable to the levels detected in naturally infected individuals nine months post-symptoms onset. These non-neutralizing antibodies mostly act as ‘danger flags,’ alerting the immune system of the infection.
In individuals with a history of COVID-19, a single dose boosted both the humoral and cellular responses. A SARS-CoV-2 specific cellular immune response was noted following vaccination in individuals both with and without prior exposure to COVID-19, although it was more significant in the group with exposure. These results suggest that individuals without prior SARS-CoV-2 exposure would benefit the most from receiving two doses of the vaccine.
The authors conclude that vaccination of individuals without prior exposure to SARS-CoV-2 results in specific humoral and cellular immune responses similar to the ones observed after a natural infection, which was shown to confer up to 80% protection against re-infection. They support the concept of increasing the interval between the first and second dose of the vaccines in the context of vaccine shortage to maximize protection of a larger proportion of the population.