The paucity of information on longevity of vaccine-induced immune responses and uncertainty of the correlates of protection hinder the development of evidence-based COVID-19 vaccination policies for new birth cohorts. Here, to address these knowledge gaps, we conducted a cohort study of healthy 5–12-year-olds vaccinated with BNT162b2. We serially measured binding and neutralizing antibody titers (nAbs), spike-specific memory B cell (MBC) and spike-reactive T cell responses over 1 year. We found that children mounted antibody, MBC and T cell responses after two doses of BNT162b2, with higher antibody and T cell responses than adults 6 months after vaccination. A booster (third) dose only improved antibody titers without impacting MBC and T cell responses. Among children with hybrid immunity, nAbs and T cell responses were highest in those infected after two vaccine doses. Binding IgG titers, MBC and T cell responses were predictive, with T cells being the most important predictor of protection against symptomatic infection before hybrid immunity; nAbs only correlated with protection after hybrid immunity. The stable MBC and T cell responses over time suggest sustained protection against symptomatic SARS-CoV-2 infection, even when nAbs wane. Booster vaccinations do not confer additional immunological protection to healthy children.

由于缺乏关于疫苗诱导的免疫反应寿命的信息以及保护相关性的不确定性，阻碍了针对新生儿群体制定基于证据的 COVID-19 疫苗接种政策。为了解决这些知识差距，我们对接种 BNT162b2 的健康 5-12 岁儿童进行了一项队列研究。我们在一年多的时间里连续测量了结合和中和抗体滴度 (nAb)、尖峰特异性记忆 B 细胞 (MBC) 和尖峰反应性 T 细胞反应。我们发现，儿童在接种两剂 BNT162b2 后出现了抗体、MBC 和 T 细胞反应，并且在接种疫苗 6 个月后，其抗体和 T 细胞反应高于成人。加强剂量（第三次）仅提高抗体滴度，而不影响 MBC 和 T 细胞反应。在具有混合免疫的儿童中，在接种两剂疫苗后感染的儿童中，nAb 和 T 细胞反应最高。结合 IgG 滴度、MBC 和 T 细胞反应具有预测性，其中 T 细胞是混合免疫之前针对症状感染的最重要的预测因子； nAb 仅与混合免疫后的保护作用相关。随着时间的推移，稳定的 MBC 和 T 细胞反应表明，即使 nAb 减弱，也能持续抵御有症状的 SARS-CoV-2 感染。加强疫苗接种不会为健康儿童提供额外的免疫保护。