Patterns in Repeat Reinfections: Pre and Post Omicron Emergence

Our understanding of SARS-CoV-2 reinfection patterns remains limited. We conducted a longitudinal study using Qatar’s national SARS-CoV-2 data from February 28, 2020 to June 11, 2023 to investigate incidence of reinfections both prior to and after omicron emergence. The latter analysis excluded individuals with pre-omicron infections. Before omicron introduction, the proportion of incident infections classified as reinfections gradually increased but remained minimal, reaching 1.8% just before omicron emerged. During the first omicron wave, this proportion reached 9.0%, a 5-fold increase. After the conclusion of the first omicron wave, the proportion of incident infections identified as reinfections rapidly increased, reaching 43.3% towards the end of the study. In the pre-omicron era, a total of 3,131 reinfections were documented, of which 99.6% were first reinfections and 0.4% were second reinfections. Meanwhile, a total of 20,962 reinfections were documented after an omicron primary infection of which 99.0% were first reinfections, 1.0% were second reinfections, and 0.01% were third reinfections. Reinfections were rare before omicron’s emergence but became widespread during the omicron era, including among individuals previously infected with omicron. Our findings may indicate accelerated viral evolution in the omicron era aimed at evading population immunity, but with minimal impact on COVID-19 severity, or potentially suggest immune imprinting effects that require further investigation. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The authors are grateful for support from the Biomedical Research Program and the Biostatistics, Epidemiology, and Biomathematics Research Core, both at Weill Cornell Medicine-Qatar, as well as for support provided by the Ministry of Public Health, Hamad Medical Corporation, and Sidra Medicine. The authors are also grateful for the Qatar Genome Programme and Qatar University Biomedical Research Center for institutional support for the reagents needed for the viral genome sequencing. Statements made herein are solely the responsibility of the authors. The funders of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the article. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The institutional review boards at Hamad Medical Corporation and Weill Cornell Medicine in Qatar approved this retrospective study with a waiver of informed consent. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The dataset of this study is a property of the Qatar Ministry of Public Health that was provided to the researchers through a restricted-access agreement that prevents sharing the dataset with a third party or publicly. The data are available under restricted access for preservation of confidentiality of patient data. Access can be obtained through a direct application for data access to Her Excellency the Minister of Public Health (https:// www.moph.gov.qa/english/OurServices/eservices/Pages/Governmental-HealthCommunication-Center.aspx). The raw data are protected and are not available due to data privacy laws. Aggregate data are available within the paper and its supplementary information.