Figure 2.

Adjusted vaccine effectiveness for boosted enrollees compared with those not boosted as a function of the months between primary vaccine and receipt of booster. The highest effectiveness was in boosters received 6 to 7, 7 to 8, or 8 to 9 months after the original vaccination, while intervals of less than 6 months or greater than 9 months had lower effectiveness. Error bars indicate 95% CIs. The number of enrollees, hospitalizations, hospitalization rates, and adjusted hazard ratios for each interval are given in Supplemental Table 2.