ABSTRACT
During the first period of the Covid-19 pandemic, most of the immunological studies on SARS-CoV-2 were based on hospitalized-and intensive care unit patients. In this study, a healthy population continuously exposed to the virus, Swedish primary health care workers (n = 156), were monitored for 6 months and the development of antibody patterns and T-cell responses to SARS-CoV-2 were evaluated. In addition to blood sampling, demographic-and clinical information such as PCR-tests, self-reported symptoms, underlying medical conditions, and medications were collected. Multivariate statistical analysis using OPLS-DA showed that Covid-19 infection was associated with SARS-CoV-2 specific IgG antibodies, T-cell responses, male sex, hypertension, and higher BMI and contrary, that not contracting the infection, was associated with female sex, no-or only SARS-CoV-2 specific IgA antibodies, smoking and airborne allergy. Analysis with Cytometry by Time-of-flight (CyTOF) revealed a unique cytotoxic CD4+ T cell population in participants with IgG-dominated antibody responses which expressed CD25, CD38, CD69, CD194, CD279, CTLA-4 and granzyme B. 10% of the study participants had only SARS-CoV-2 specific IgA antibodies with no detectable SARS-CoV-2 specific IgG antibodies. These IgA antibodies could partially neutralize the virus in vitro and none of the participants with this antibody pattern contracted Covid-19 during the study period. These results have the potential to further help us understand the immunological responses to SARS-CoV-2 infection.