CFB and infection: Interestingly, compared to N- vaccinees, CS tended to induce lower nAb to both BA.1 and BA.2, while CO failed to induce a significant increase in nAb to Omicron variants in N+ vaccinees (Fig. 5d, f, Supplementary Fig. 4g–j), highlighting that ongoing infection and/recent exposure to a circulating variant can potentially dampen rather than enhance vaccine immunogenicity reflective of potential antigenic competition.