The study demonstrated the capacity of a third dose to broaden antibody-based immunity and boost protection against circulating variants of concern. However, it is interesting that neutralizing responses against the Beta variant, known to markedly escape vaccine-elicited antibody responses4, were only fractionally better in those receiving a Beta-specific booster immunization.

Interestingly, all four vaccine breakthrough infection subjects who had previous COVID-19 were seropositive for anti-membrane IgG during acute infection, while no breakthrough subjects without prior COVID-19 had detectable anti-membrane antibodies in the acute infection period (Figure 1I).