Fig. 2

The GMC of booster vaccination. Geometric mean concentration (GMC) was derived by transforming the antibody titer by log10. At day 0, the statistical comparison was between all four groups; at 14 days after booster and month 6, the statistical comparison was between the groups with the same primary vaccination regimen or the same booster dose. *P > 0.05, **P < 0.05, ***P < 0.001.