2.2. Data collection

The following baseline characteristics were taken into account: preventive measures (flu vaccination in 2019); the presence of major chronic conditions or risk factors such as immunodeficiency, coronary artery disease, high blood pressure, diabetes, chronic kidney disease, history of stroke, hyperlipidemia or obesity (BMI > 30 kg/m²); and, gender, age, country of origin (Spain vs other), living in nursing homes, number of cohabitants and degree of dependency as possible socioeconomic and demographics confounding factors.

Two principal endpoints were considered along the follow-up: risk of SARS-CoV-2 infection in the whole susceptible study population (considered when a PCR positive test was registered); and SARS-CoV-2 prognosis: risk of hospitalization, ICU admission or death in those who had been infected.