The effectiveness of the coronavirus disease 2019 (COVID-19) BNT162b2 vaccine in preventing disease and reducing viral loads of breakthrough infections (BTIs) has been decreasing, concomitantly with the rise of the Delta variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, it is unclear whether the observed decreased effectiveness of the vaccine in reducing viral loads is inherent to the Delta variant or is dependent on time from immunization. By analyzing viral loads of over 16,000 infections during the current, Delta-variant-dominated pandemic wave in Israel, we found that BTIs in recently fully vaccinated individuals have lower viral loads than infections in unvaccinated individuals. However, this effect starts to decline 2 months after vaccination and ultimately vanishes 6 months or longer after vaccination. Notably, we found that the effect of BNT162b2 on reducing BTI viral loads is restored after a booster dose. These results suggest that BNT162b2 might decrease the infectiousness of BTIs even with the Delta variant, and that, although this protective effect declines with time, it can be restored, at least temporarily, with a third, booster, vaccine dose.

2019 年冠状病毒病 (COVID-19) BNT162b2 疫苗在预防疾病和减少突破性感染 (BTI) 的病毒载量方面的有效性一直在下降，同时严重急性呼吸综合征冠状病毒 2 (SARS-CoV) 的 Delta 变体的增加-2)。然而，尚不清楚观察到的疫苗在减少病毒载量方面的有效性降低是 Delta 变体固有的还是取决于免疫接种时间。通过分析以色列当前以 Delta 变体为主的大流行浪潮中超过 16,000 例感染的病毒载量，我们发现最近完全接种疫苗的个体中的 BTI 的病毒载量低于未接种疫苗的个体的病毒载量。然而，这种影响在接种疫苗后 2 个月开始下降，最终在接种疫苗后 6 个月或更长时间消失。值得注意的是，我们发现 BNT162b2 降低 BTI 病毒载量的作用在加强剂量后恢复。这些结果表明，即使使用 Delta 变体，BNT162b2 也可能降低 BTI 的传染性，尽管这种保护作用会随着时间的推移而下降，但至少暂时可以通过第三剂加强疫苗来恢复。