The risk of symptomatic reinfection during the second COVID-19 wave in individuals previously exposed to SARS-CoV-2

Manica, M.; Pancheri, S.; Poletti, P.; Giovanazzi, G.; Guzzetta, G.; Trentini, F.; Marziano, V.; Ajelli, M.; Zuccali, M. G.; Benetollo, P. P.; Merler, S.; Ferro, A.

To what extent infection with SARS-CoV-2 protects against subsequent reinfection or symptomatic reinfection is still unclear. In this cohort study, we analyzed surveillance records of COVID-19 cases identified between June 2020 and January 2021 in five Italian municipalities, where 77.7% of the entire population was screened for IgG antibodies in May 2020. We compared the risk of observing symptomatic infections in two mutually exclusive groups defined by the initial serological response. We estimated that the cumulative incidence of identified symptomatic infections in the IgG negative and positive cohorts was 2.67% (95%CI: 2.12%-3.37%) and 0.14% (95%CI: 0.04%-0.58%), respectively. The adjusted odd ratio of developing symptomatic infection in individuals previously exposed to SARS-CoV-2 was estimated at 0.054 (95%CI: 0.009-0.169). Quantifying protective immunity against COVID-19 disease elicited by natural infection with SARS-CoV-2 is essential to inform strategies for controlling the pandemic in the forthcoming months.