Limitations of the study: Although this study uses pseudotyped virus assays, rather than authentic virus, very good correlation was established between the two assays and with protection from challenge (Arunachalam et al., 2021;Case et al2020b). This study is based on cohorts of
15 individuals or fewer and may be limited by sample size. Finally, we emphasize that our study
is focused on serum antibody responses and that other aspects of the immune system participate
in controlling viral infections, including memory B cells and T cells