Objectives This cohort study including essential workers, assessed the risk and incidence of SARS-CoV-2 infection during the second surge of COVID-19 according to baseline serostatus and occupational sector.
Methods Essential workers were selected from a seroprevalence survey cohort in Geneva, Switzerland and were linked to a state centralised registry compiling SARS-CoV-2 infections. Primary outcome was the incidence of virologically confirmed infections from serological assessment (between May and September 2020) to 25 January 2021, according to baseline antibody status and stratified by three predefined occupational groups (occupations requiring sustained physical proximity, involving brief regular contact or others).
Results 10 457 essential workers were included (occupations requiring sustained physical proximity accounted for 3057 individuals, those involving regular brief contact, 3645 and 3755 workers were classified under ‘Other essential occupations’). After a follow-up period of over 27 weeks, 5 (0.6%) seropositive and 830 (8.5%) seronegative individuals had a positive SARS-CoV-2 test, with an incidence rate of 0.2 (95% CI 0.1 to 0.6) and 3.2 (95% CI 2.9 to 3.4) cases per person-week, respectively. Incidences were similar across occupational groups. Seropositive essential workers had a 93% reduction in the hazard (HR of 0.07, 95% CI 0.03 to 0.17) of having a positive test during the follow-up with no significant between-occupational group difference.
Conclusions A 10-fold reduction in the hazard of being virologically tested positive was observed among anti-SARS-CoV-2 seropositive essential workers regardless of their sector of occupation, confirming the seroprotective effect of a previous SARS-CoV2 exposure at least 6 months after infection.
- occupational health
Data availability statement
Data are available on reasonable request.
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AL, AB, IG and SS contributed equally.
Collaborators SEROCoV-WORK + Study Group: Victoria Alber, Isabelle Arm-Vernez, Andrew S. Azman, Delphine Bachmann, Donatien Bachmann, Stéphanie Baggio, Jean-François Balavoine, Gil Barbosa Monteiro, Hélène Baysson, Patrick Bleich, Isabelle Boissel, François Chappuis, Prune Collombet, Delphine Courvoisier, Philippine Couson, Alioucha Davidovic, Clement Deiri, Divina Del Rio, Carlos de Mestral, David De Ridder, Yaron Dibner, Paola D’Ippolito, Joséphine Duc, Roxane Dumont, Isabella Eckerle, Nacira El Merjani, Gwennaelle Ferniot, Antonie Flahault, Natalie Francioli, Marion Frangville, Carine Garande, Laurent Gétaz, Pamela Giraldo, Fanny Golaz, Julie Guérin, Idris Guessous, Ludivine Haboury, Séverine Harnal, Victoria Javet, Laurent Kaiser, Omar Kherad, Amélie Laboulais, Gaëlle Lamour, Xavier Lefebvre, Pierre Lescuyer, Andrea Jutta Loizeau, Fanny-Blanche Lombard, Elsa Lorthe, Chantal Martinez, Kourosh Massiha, Ludovic Metral-Boffod, Benjamin Meyer, Khaled Mostaguir, Mayssam Nehme, Natacha Noël, Nicolas Oederlin, Francesco Pennacchio, Javier Perez-Saez, Dusan Petrovic, Attilio Picazio, Didier Pittet, Giovanni Piumatti, Jane Portier, Géraldine Poulain, Caroline Pugin, Nick Pullen, Barinjaka Rakotomiaramanana, Zo Francia Randrianandrasana, Aude Richard, Viviane Richard, Sabina Rodriguez-Velazquez, Lilas Salzmann-Bellard, Silvia Stringhini, Leonard Thorens, Simon Torroni, Didier Trono, David Vidonne, Guillemette Violot, Nicolas Vuilleumier, Zoé Waldmann, Manon Will, Ania Wisniak, Sabine Yerly & María-Eugenia Zaballa
Contributors The idea for the study originally came from AL. AL and AB carried out the literature search. AL, AB, SS, IG, RDum, RDub, ASA and MEZ conceptualised and designed the study. GP and DSC oversaw database linkage. AB and FK conducted clinical investigations. RDum and RDub did data analysis. AL, AB, SS and ASA wrote the first draft of the manuscript. All authors have read, critically revised and approved the final version of this manuscript. AL and AB, SS and IG contributed equally to this paper.
Funding This study was funded by the Private Foundation of the Geneva University Hospitals, the Fondation des Grangettes and the Centre for Emerging Viral Diseases.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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