Fig. 1.

(A) Mean inhibition rates in HCP by sampling period, (B) inhibition rates in selected individuals that had negative neutralization ability before booster dose Error Bars 95% CI.

Sampling 1: samples collected approximately 3 months after the second vaccine dose (mean: 95.3 days, range: 52–135 days). Sampling 2: samples collected approximately 6 months after the second vaccine dose (mean: 184.6 days, range: 136–225 days). Sampling 3: samples collected approximately 9 months after the second vaccine dose (mean: 262.9 days, range: 226–322 days). The effect of booster dose was estimated approximately 3 weeks after the booster dose (mean 21.5 days, range: 7–55 days) HCP: healthcare personnel; CI: confidence interval