This evidence synthesis has been compiled by members of the CITF Secretariat and does not necessarily represent the views of all CITF members.

By Jeanie Quach

Reinfections in UK health-care workers

A large, national, multicentre prospective cohort study of hospital healthcare workers in the UK (The SARS-CoV-2 Immunity and Reinfection Evaluation, SIREN) reports, in an interim analysis published in The Lancet, that participants who previously had SARS-CoV-2 antibodies had an 84% lower risk of (re)infection. This is comparable to the protection offered by currently approved vaccines. The protective effect was observed seven months following primary infection, although the study is still ongoing.

Understanding the nature and rate of SARS-CoV-2 reinfection is critical during this pandemic as it will guide informed public health decisions. This interim analysis from the UK included 25,661 health-care workers, support staff, and administrative staff recruited from June 18 to December 31, 2020 and was performed after seven months of follow-up. Participants were assigned to either the positive cohort (antibody positive, or previous positive SARS-CoV-2 PCR or antibody test) or a negative cohort. Follow-ups included questionnaires on symptoms and exposure, SARS-CoV-2 antibody testing and PCR to determine reinfections.

In the positive cohort, 155 new infections (or reinfections) were detected versus 1704 new PCR-positive infections in the negative cohort. The number of cases was 7.6 reinfections per 100,000 person-days in the positive cohort, compared with 57.3 primary infections per 100,000 person-days in the negative cohort. The effects of vaccines and the spread of the variant originating from the UK has been taken into consideration in these analyses.

Authors conclude that primary infection with SARS-CoV-2 provides immunity against reinfection in the short- to medium-term and this is comparable to protection against symptomatic infection with currently approved vaccines.

Hall VJ, Foulkes S, Charlett A, Atti A, Monk EJM, Simmons R, Wellington E, Cole MJ, Saei A, Oguti B, Munroe K, Wallace S, Kirwan PD, Shrotri M, Vusirikala A, Rokadiya S, Kall M, Zambon M, Ramsay M, Brooks T, Brown CS, Chand MA, Hopkins S, and the SIREN Study Group Hall. SARS-CoV-2 infection rates of antibody-positive compared with antibody-negative health-care workers in England: a large, multicentre, prospective cohort study (SIREN). The Lancet. 2021 Apr 9;397(10283):1459-1469. doi: 10.1016/S0140-6736(21)00675-9

Canadian study assessing reinfections in health-care workers

A CITF-funded study titled “REinfection in COVID-19 Estimation of Risk (RECOVER)” led by researcher Dr. Caroline Quach from CHU Sainte-Justine, is also studying health-care workers to estimate the risk of reinfection with SARS-CoV-2 over 12 months of follow-up. Recruitment is being done through the McGill University Health Centre Vaccine Center, CHU Sainte-Justine, CHUM, and Jewish General Hospital. Analyses include studying the kinetics of antibodies, specific T cell responses, viral loads and viral strains.