Risk of Reinfection After Seroconversion to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2): A Population-based Propensity-score Matched Cohort Study
Authors: Leidi Antonio , Koegler Flora , Dumont Roxane , Dubos Richard , Zaballa María-Eugenia , Piumatti Giovanni , Coen Matteo , Berner Amandine , Darbellay Farhoumand Pauline , Vetter Pauline , Vuilleumier Nicolas , Kaiser Laurent , Courvoisier Delphine , Azman Andrew S , Guessous Idris , Stringhini Silvia ,   SEROCoV-POP study group, Ferrillo Sabine Yerly , Schibler Manuel , Tardin Aglaé , Genecand Camille , Stringhini Silvia , Guessous Idris , Azman Andrew S , Baysson Hélène , Collombet Prune , De Ridder David , d’Ippolito Paola , Rinella Matilde D’asaro-Aglieri , Dibner Yaron , El Merjani Nacira , Francioli Natalie , Frangville Marion , Marcus Kailing , Martinez Chantal , Noel Natacha , Pennacchio Francesco , Perez-Saez Javier , Petrovic Dusan , Picazio Attilio , Pishkenari Alborz , Piumatti Giovanni , Portier Jane , Pugin Caroline , Rakotomiaramanana Barinjaka , Richard Aude , Salzmann-Bellard Lilas , Schrempft Stephanie , Zaballa Maria-Eugenia , Waldmann Zoé , Wisniak Ania , Davidovic Alioucha , Duc Joséphine , Guérin Julie , Lombard Fanny , Will Manon , Flahault Antoine , Vernez Isabelle Arm , Keiser Olivia , Mattera Loan , Schellongova Magdalena , Kaiser Laurent , Eckerle Isabella , Lescuyer Pierre , Meyer Benjamin , Poulain Géraldine , Vuilleumier Nicolas , Yerly Sabine , Chappuis François , Welker Sylvie , Courvoisier Delphine , Gétaz Laurent , Nehme Mayssam , Pardo Febronio , Violot Guillemette , Hurst Samia , Matute Philippe , Maugey Jean-Michel , Pittet Didier , L’Huillier Arnaud G , Posfay-Barbe Klara M , Pradeau Jean-François , Tacchino Michel , Trono Didier 
Published: May 2021

Abstract

Background
Serological assays detecting anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies are being widely deployed in studies and clinical practice. However, the duration and effectiveness of the protection conferred by the immune response remains to be assessed in population-based samples. To estimate the incidence of newly acquired SARS-CoV-2 infections in seropositive individuals as compared to seronegative controls, we conducted a retrospective longitudinal matched 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. Seropositive participants were matched one-to-two to seronegative controls, using a propensity-score including age, gender, 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 outcome was confirmed infections occurring from serological status assessment to the end of the second pandemic wave (January 2021).

Results
Among 8344 serosurvey participants, 498 seropositive individuals were selected and matched with 996 seronegative controls. After a mean follow-up of 35.6 (standard deviation [SD] 3.2) weeks, 7 out of 498 (1.4%) seropositive subjects had a positive SARS-CoV-2 test, of whom 5 (1.0%) were classified as reinfections. In contrast, the infection rate was higher in seronegative individuals (15.5%, 154/996) during a similar follow-up period (mean 34.7 [SD 3.2] weeks), corresponding to a 94% (95% confidence interval [CI]: 86%– 98%, P &lt; .001) reduction in the hazard of having a positive SARS-CoV-2 test for seropositives.

Conclusions
Seroconversion after SARS-CoV-2 infection confers protection against reinfection lasting at least 8 months. These findings could help global health authorities establishing priority for vaccine allocation.