Current COVID-19 vaccines significantly reduce overall morbidity and mortality and are vitally important to controlling the pandemic. Individuals who previously recovered from COVID-19 have enhanced immune responses after vaccination (hybrid immunity) compared to their naïve-vaccinated peers; however, the effects of post-vaccination breakthrough infections on humoral immune response remain to be determined. Here, we measure neutralizing antibody responses from 104 vaccinated individuals, including those with breakthrough infections, hybrid immunity, and no infection history. We find that human immune sera following breakthrough infection and vaccination following natural infection, broadly neutralize SARS-CoV-2 variants to a similar degree. While age negatively correlates with antibody response after vaccination alone, no correlation with age was found in breakthrough or hybrid immune groups. Together, our data suggest that the additional antigen exposure from natural infection substantially boosts the quantity, quality, and breadth of humoral immune response regardless of whether it occurs before or after vaccination.

SARS-CoV-2 and its variants continue to infect hundreds of thousands every day despite the rollout of effective vaccines. Therefore, it is essential to understand the levels of protection that these vaccines provide in the face of emerging variants. Here, we report two demographically balanced cohorts of BNT162b2 vaccine recipients and COVID-19 patients, from which we evaluate neutralizing antibody titers against SARS-CoV-2 as well as the B.1.1.7 (alpha) and B.1.351 (beta) variants. We show that both B.1.1.7 and B.1.351 are less well neutralized by serum from vaccinated individuals, and that B.1.351, but not B.1.1.7, is less well neutralized by convalescent serum. We also find that the levels of variant-specific anti-spike antibodies are proportional to neutralizing activities. Together, our results demonstrate the escape of the emerging SARS-CoV-2 variants from neutralization by serum antibodies, which may lead to reduced protection from re-infection or increased risk of vaccine breakthrough.

Vaccination with 2 doses of the BNT162b2 vaccine (Pfizer-BioNTech) reportedly provides 95% protection from COVID-19. 1 However, patient age is known to contribute to the risk of COVID-19 incidence and severity. 2 We examined the relationship between age and neutralizing antibody titers against the early SARS-CoV-2 USA-WA1/2020 strain and the P.1 variant of concern after 2 doses of the BNT162b2 vaccine.Methods | The Oregon Health & Science University conducted large-scale vaccination of all workforce members in accordance with Oregon vaccination guidelines between December 2020 and February 2021. Individuals were enrolled in this study during their first vaccination visit and serum samples were collected prior to receipt of the first dose and 14 days after receipt of the second dose of the BNT162b2 vaccine. Study participants were selected randomly from a larger vaccine study cohort to maintain equal sex and age distribution.SARS-CoV-2 spike receptor-binding domain-specific antibody levels were measured by enzyme-linked immunosorbent assays, and 50% effective titers (EC 50 ) were calculated. SARS-CoV-2 50% neutralizing titers were determined by focus reduction neutralization tests (FRNT 50 ) using live clinical isolates of the original SARS-CoV-2 strain (USA-WA1/2020) and the P.1 variant. Associations between age and EC 50 and FRNT 50 were determined by fitting a linear model to log-transformed data in Graphpad Prism, version 9.0.2. Two-tailed P values were calculated by F test with a zero-slope null hypothesis and a significance cutoff of P≤.05.This study was performed in accordance with the institutional review board at Oregon Health & Science University. Written informed consent was obtained from participants. Additional method details of the serum collection and laboratory analyses can be found in the eAppendix in the Supplement.

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We tested human sera from large, demographically balanced cohorts of BNT162b2 vaccine recipients (n=51) and COVID-19 patients (n=44) for neutralizing antibodies against SARS-CoV-2 variants B.1.1.7 and B.1.351. Although the effect is more pronounced in the vaccine cohort, both B.1.1.7 and B.1.351 show significantly reduced levels of neutralization by vaccinated and convalescent sera. Age is negatively correlated with neutralization in vaccinee, and levels of variant-specific RBD antibodies are proportional to neutralizing activities.