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.

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.

Inclusion Criteria:

• All PCR- or RAT-confirmed SARS-CoV-2 reinfections were included in the study.

Exclusion Criteria:

• Patients who did not know if they were reinfected were excluded.

A Primary SARS-CoV-2 infection was defined as having a positive PCR test result for the first time. A suspect SARS-CoV-2 reinfection (generally referred as reinfection in this paper) was defined as having a positive PCR of RAT sample over 90 days following primary infection.

Individual participant data (including data dictionaries) will be available. Individual participant data that underlie the results reported in this article will be shared after de-identification (text, tables, figures, and appendices). Study protocol will also be available. The time period for data sharing begins nine months and ends 36 months following article publication. Data is available with investigators whose proposed use of the data has been approved by an independent review committee ("learned intermediary") identified for individual participant data meta-analysis. Proposals may be submitted up to 36 months following article publication. After 36 months the data will be available in our university's data warehouse but without investigator support other than deposited metadata. Information regarding submitting proposals and accessing data may be found at https://yxky.fudan.edu.cn.

The time period for data sharing begins nine months and ends 36 months following article publication.

Data is available with investigators whose proposed use of the data has been approved by an independent review committee ("learned intermediary") identified for individual participant data meta-analysis.