Serology study after BTN162b2 vaccination in participants previously infected with SARS-CoV-2 in two different waves versus naïve

The antibody response to SARS-CoV-2 mRNA vaccines in individuals with waning immunity generated by a previous SARS-CoV-2 infection, as well as the patterns of IgA and IgM responses in previously infected and in naive individuals are still poorly understood. We performed a serology study in a cohort of BTN162b2 mRNA vaccine recipients who were immunologically naive (N, n = 50) or had been previously infected with SARS-CoV-2 (P.I., n = 51) during the first (n = 25) or second (n = 26) pandemic waves in Italy, respectively. We measured IgG, IgM and IgA antibodies against the SARS-CoV-2 Spike (S) and IgG against the nucleocapsid (N) proteins, as well as the neutralizing activity of sera collected before vaccination, after the first and second dose of vaccine. Most P.I. individuals from the first pandemic wave who showed declining antibody titres responded to the first vaccine dose with IgG-S and pseudovirus neutralization titres that were significantly higher than those observed in N individuals after the second vaccine dose. In all recipients, a single dose of vaccine was sufficient to induce a potent IgA response that was not associated with serum neutralization titres. We observed an unconventional pattern of IgM responses that were elicited in only half of immunologically naive subjects even after the second vaccine dose. The response to a single dose of vaccine in P.I. individuals is more potent than that observed in N individuals after two doses. Vaccine-induced IgA are not associated with serum neutralization. Dalle Carbonare et al. perform a serology study in participants with a prior infection of SARS-CoV-2 and those who are SARS-CoV-2-naive, who received two doses of the Pfizer-BioNTech BNT162b2 vaccine. After a single dose they observe a quicker recall of pseudovirus neutralization titres in previously-infected participants and a potent IgA response in both groups that was not associated with serum neutralization titres. Antibodies are proteins produced by the immune system that are released into the bloodstream and help fight infections. To understand how the immune system responds to COVID-19 vaccination in individuals who have had a previous SARS-CoV-2 infection, we compared the types and levels of antibodies produced after first and second doses of the vaccine with those of individuals who had never been infected. We found that one dose of vaccine, even several months after the infection, was sufficient to boost a very efficient response by eliciting specific types of antibodies, some of which were and some that were not able to neutralize the virus. We also observed an unusual antibody profile in almost half of individuals who had not been infected. These findings may help better understand the immune response to COVID-19 vaccines.