ABSTRACT
Sparse data exist on the complex natural immunity to SARS-CoV-2 at the population level. We applied a well-validated multiplex serology test in 5000 participants of a general population study in Catalonia in blood samples collected from end June to mid November 2020. Based on responses to fifteen isotype-antigen combinations, we detected a seroprevalence of 18.1% in adults (n=4740), and modeled extrapolation to the general population of Catalonia indicated a 15.3% seroprevalence. Antibodies persistedup to 9 months after infection. Immune profiling of infected individuals revealed that with increasing severity of infection (asymptomatic, 1-3 symptoms, ≥4 symptoms, admitted to hospital/ICU), seroresponses were more robust and rich with a shift towardsIgG over IgA and anti-spike over anti-nucleocapsid responses. Among seropositive participants, lower antibody levels were observed for those ≥60 years vs <60 years old and smokers vs non-smokers. Overweight/obese participants vs normal weight had higher antibody levels. Adolescents (13-15 years old) (n=260) showed aseroprevalence of 11.5%, were less likely to be tested seropositive compared to their parentsand had dominant anti-spike rather than anti-nucleocapside IgG responses. Our study provides an unbiased estimate of SARS-CoV-2 seroprevalence in Catalonia and new evidence on the durability and heterogeneity of post-infection immunity.