Distinct neutralizing kinetics and magnitudes elicited by different SARS-CoV-2 variant spikes

The rapid evolution of SARS-CoV-2 mandates a better understanding of cross-protection between variants after vaccination or infection, but studies directly evaluating such cross-protection are lacking. Here we report that immunization with different variant spikes elicits distinct neutralizing kinetics and magnitudes against other SARS-CoV-2 variants. After immunizing hamsters with wild-type or mutant SARS-CoV-2 bearing variant spikes from Alpha, Beta, Gamma, or Epsilon, the animals developed faster and greater neutralization activities against homologous SARS-CoV-2 variants than heterologous variants, including Delta. The rank of neutralizing titers against different heterologous variants varied, depending on the immunized variant spikes. The differences in neutralizing titers between homologous and heterologous variants were as large as 62-, 15-, and 9.7-fold at days 14, 28, and 45 post-immunization, respectively. Nevertheless, all immunized hamsters were protected from challenges with all SARS-CoV-2 variants, including those exhibiting the lowest neutralizing antibody titers. The results provide insights into the COVID-19 vaccine booster strategies.