Prevalence and risk factors of SARS-CoV-2 antibody responses among healthcare workers (June 2020-November 2021).

"Conflicts of interest : None declared."

"Funding This study was funded by a grant from the Catalan Parliament to promote Covid-19 studies with code 2020-5100-IIIP-0032 and from Fundació Privada Salut del Consorci Sanitari del Maresme under the campaign: Impulsem la Recerca. https://impulsemlarecerca.csdm.cat/. Conflicts of interest: None declared."

"This observational and prospective study followed the cohort of all 2455 active CSdM workers from June 2020 to November 2021. All of them were informed about the study and invited to participate by e-mail and by announcements on the CSdM website. Once workers gave their informed consent, they answered an electronic self-administered questionnaire on personal sociodemographic, clinical and labor characteristics through the CSdM website, and scheduled a blood extraction for serological tests. This procedure was carried out in June 2020, October 2020, April 2021 and November 2021. Participation rates in the seroprevalence study were 77.9%, 77.1%, 84.3% and 68.9% of the total target population, respectively. Most CSdM workers (88.8%) received two doses of vaccine from January to March 2021, all of them with mRNA vaccines (74.4% Moderna COVID-19 Vaccine, Moderna Biotech Spain, 25.6% Comirnaty BioNTech, Pfizer). A figure in gives the epidemiological time context, showing the number of confirmed cases of COVID-19 treated at Mataró hospital from March 2020 to January 2022, the various phases of the study and the vaccination periods (first, second and third doses). The study protocol was approved by the Ethics Committee (CEIm, CSdM 56/20). The study was conducted according to the principles and rules stated in the Declaration of Helsinki and following the regulations established by Spanish biomedical research law (LIB 14/2007), the Spanish law of protection of personal data (LOPD 3/2018) and Regulation (EU) 2016/679 of the EU Parliament and of the Council of 27th April 2016. The study was registered in the ClinicalTrials.gov website under code: NCT04425759."