Andorra is a small country located in the Pyrenees attracting millions of visitors, mainly for ski tourism. We estimated SARS-CoV-2 seroprevalence in the entire country by universal serological testing. From 4–28 May, 2020 two cross sectional serological surveys were conducted using a rapid serological test (nCOV IgG/IgM). 72,964 inhabitants (96.1% of the population) participated. Overall seroprevalence was 11.0%. The odds of being seropositive was higher among seasonal workers (OR 1.87; 95% CI 1.57–2.23), students (OR 1.64; 95% CI 1.48–1.82) or in the population living in La Massana region (OR 2.65; 95% CI 2.43–2.89). A higher seroprevalence was observed in those familiar nuclei with greater numbers of cohabitants: 18% in families with 6 household members or more; 13% in medium size families (3/4/5 people) and 12% in small size (1 to 2 people) nuclei (p < 0.001). Seasonal workers, students and inhabitants based in ski-related areas presented a higher seroprevalence. Mass antibody screening allows to identify infection hotspots and should contribute to the design of tailored interventions to prevent SARS-CoV-2 transmission.

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