Antibodies elicited by SARS-CoV-2 infection and boosted by vaccination neutralize an emerging variant and SARS-CoV-1

The emergence of SARS-CoV-2 variants raises concerns about their resistance to neutralizing antibodies elicited from previous infection, or from vaccination. Here we examined whether sera and monoclonal antibodies from convalescent donors, prior to and following a single immunization with the Pfizer or Moderna mRNA vaccines, neutralize the Wuhan-Hu-1 strain and a variant, B.1.351 from South Africa. Pre-vaccination sera weakly neutralized Wuhan-Hu-1 and sporadically neutralized B.1.351. Immunization with either vaccine generated anamnestic B and CD4+ T cell responses and a 1000-fold increase in neutralizing antibody titers against both strains and SARS-CoV-1. Neutralization was likely due to anti-RBD and anti-S2 antibodies. Our study highlights the importance of vaccination of both uninfected and of previously infected subjects, as the elicited immune response will neutralize distinct viral strains.