Dynamics of Naturally Acquired Immunity Against Severe Acute Respiratory Syndrome Coronavirus 2 in Children and Adolescents

Abstract

To evaluate the duration of protection against reinfection conferred by a previous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in children and adolescents. We applied 2 complementary approaches: a matched test-negative, case-control design and a retrospective cohort design. A total of 458 959 unvaccinated individuals aged 5-18years were included. The analyses focused on the period July 1, 2021, to December 13, 2021, a period of Delta variant dominance in Israel. We evaluated 3 SARS-CoV-2-related outcomes: documented polymerase chain reaction-confirmed infection or reinfection, symptomatic infection or reinfection, and SARS-CoV-2-related hospitalization or death. Overall, children and adolescents who were previously infected acquired durable protection against reinfection with SARS-CoV-2 for at least 18months. Importantly, no SARS-CoV-2-related deaths were recorded in either the SARS-CoV-2-naïve group or the previously infected group. The effectiveness of naturally acquired immunity against a recurrent infection reached 89.2% (95% CI, 84.7%-92.4%) at 3-6 months after the first infection and declined slightly to 82.5% (95% CI, 79.1%-85.3%) by 9-12months after infection, with a slight nonsignificant waning trend seen up to 18months after infection. Additionally, children aged 5-11years exhibited no significant waning of naturally acquired protection throughout the outcome period, whereas waning protection in those aged 12-18 years was more prominent but still mild. Children and adolescents who were previously infected with SARS-CoV-2 remain protected to a high degree for 18months. Further research is needed to examine naturally acquired immunity against Omicron and newer emerging variants.