The investigators used data from Huashan Hospital, Renji Hospital, and Shanghai Jing' an Central Hospital to collect information on SARS-CoV-2 primary infections with BA.2 during 1 March to 23 May 2022, and followed up for participants' reinfections with BA.5-lineages during 1 December 2022 to 14 January 2023. After matched 1:1 by age and gender with the reinfection cohort, data of primary infections with BA.5-sublineages were also collected. Reinfection cases were defined as having positive COVID-19 PCR or antigen test, at least 90 days after participants' first positive testing. Basic information, vaccination status, time interval between two infections, and clinical manifestations were collected.
As the COVID-19 pandemic continues and the number of individuals with previous infection rises, numbers of SARS-CoV-2 reinfection are increasing. The second Omicron wave in Shanghai, China caused by BA.5-sublineages led to a large fraction of reinfections among BA.2 primary infections. To better understand the SARS-CoV-2 reinfection rate and clinical severity of reinfections, the investigators conducted a multi-centre cohort study. The investigators hope to provide valuable clinical evidences for reinfections and offer guidance for future policy making.