Correlates of protection against symptomatic SARS-CoV-2 in vaccinated children
Youjia Zhong, Alicia Kang, Carina Jing Xuan Tay, Hui’ En Li, Nurul Elyana, Chee Wah Tan, Wee Chee Yap, Joey Ming Er Lim, Nina Le Bert, Kuan Rong Chan, Eugenia Z. Ong, Jenny G. Low, Lynette Pei‐Chi Shek, Elizabeth Huiwen Tham, Eng Eong Ooi
Abstract
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.