This is a summary, written by members of the CITF Secretariat, of:

Nantel S, Bourdin B, Adams K, Carbonneau J, Rabezanahary H, Hamelin M-E, McCormack D, Savard P, Longtin Y, Cheng MP, De Serres G, Corbeil J, Gilca V, Baz M, Boivin G, Quach C, Decaluwe H. Symptomatology during previous SARS-CoV-2 infection and serostatus before vaccination 1 influences the immunogenicity of BNT162b2 COVID-19 mRNA vaccine. Front Immunol. 2022 Oct 14;13:930252. doi: 10.3389/fimmu.2022.930252.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

Research stemming from the CITF-funded RECOVER study, published in Frontiers in Immunology, indicates that a two-dose primary series of vaccination is paramount for protection against COVID-19, even for those who were previously infected. Individuals who did not experience symptoms during their SARS-CoV-2 infection and had no antibodies to SARS-CoV-2 (negative serostatus) prior to vaccination show weaker immune responses to each vaccine dose than their symptomatic counterparts. Despite this, all participants, irrespective of whether they had been previously infected, elicited a robust immune response after a second dose of vaccine. The study is led by Drs. Caroline Quach and Hélène Decaluwe from the Sainte-Justine University Hospital and Research Centre.

Key findings:

  • Individuals previously infected with SARS-CoV-2 received a significant boost to their humoral and cellular immune responses following one vaccine dose. This entailed increased levels of antibodies targeting the receptor binding domain (RBD), antibody neutralization capacity, and markers of cell-mediated immunity (specifically, interferon gamma secretion by T-cells).
  • In contrast, uninfected individuals mounted lower levels of the above measures of immunity after one dose. In fact, only one individual in this group had detectable neutralizing antibodies.
  • The strength of the immune response following one dose was proportional to symptom severity at infection. Among recovered individuals, 69% of those who were asymptomatic mounted high RBD antibody levels, neutralizing capacity, and cell-mediated immunity after one dose compared to 92% of symptomatic individuals.
  • Those who had detectable infection-acquired antibodies six months after infection had a strong general immune response after the first dose. Comparatively, people who recovered from COVID-19 but did not have detectable infection-acquired antibodies after six months generated lower levels of RBD antibodies, neutralizing capacity, and cell-mediated immunity after one dose.
  • All participants elicited a robust immune response following two doses of vaccine.

The authors recommend that previously infected individuals who were asymptomatic complete the two-dose primary series and subsequent boosters to prevent reinfection and its complications.

A total of 55 unvaccinated healthcare workers with a previous PCR-confirmed SARS-CoV-2 infection were selected for this study based on symptomology at infection and serostatus six months after infection. A comparator group consisted of 14 unvaccinated and not previously infected healthcare workers. All individuals were vaccinated with Pfizer-BioNTech’s Comirnaty vaccine.