Risk of reinfection with SARS-CoV-2 after seroconversion: a population-based cohort study with propensity score matching

Leidi, A, Koegler F, Dumont R, Dubos R, Zaballa ME, Piumatti, G, Coen M, Berne A, Darbellay Farhoumand P, Vetter P, Vuilleumier N, Kaiser L, Courvoisier D, Azman A, Guessous I, and Stringhini S; for the SEROCoV-POP study group.
Risk of Reinfection after Seroconversion to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2): A Population-based Propensity-score Matched Cohort StudyClinical Infectious Diseases, published online 27 May 2021.doi: 10.1093/cid/ciab495

Summary: Serological tests detecting antibodies to SARS-CoV-2 are widely deployed in studies and clinical practice. However, the duration and efficacy of the protection conferred by the immune response remains to be assessed. To estimate the incidence of newly acquired SARS-CoV-2 infections in seropositive individuals compared with seronegative controls, we conducted a matched retrospective longitudinal study.

Methods: A seroprevalence survey including a representative sample of the population was conducted in Geneva, Switzerland, between April and June 2020, immediately after the first pandemic wave. HIV-positive participants were matched one to two (1:1, 1:2) to HIV-negative controls, using a propensity score including age, sex, immunodeficiency, body mass index (BMI), smoking status, and education level. Each individual was linked to a state registry of SARS-CoV-2 infections. Our primary endpoint was confirmed infections occurring from the time of serostatus assessment until the end of the second pandemic wave (January 2021).

Results: Among the 8344 participants in the seropositive survey, 498 seropositive individuals were selected and matched with 996 seronegative controls. After a mean follow-up of 35.6 weeks (standard deviation [SD] 3.2) weeks, 7 of the 498 (1.4%) seropositive subjects tested positive for SARS-CoV-2, of which 5 (1.0%) were classified as reinfections. In contrast, the rate of infection was higher in HIV-negative individuals (15.5%, 154/996) over a similar follow-up period (mean 34.7 [SD 3.2] weeks), corresponding to a 94% (95% confidence interval [CI]: 86% to 98%, P < 0.001) reduction in the risk of HIV-positive individuals testing positive for SARS-CoV-2.

Conclusion: Seroconversion after infection with SARS-CoV-2 confers protection against reinfection for at least 8 months. These results could help global health authorities prioritise vaccine allocation.

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