Objecetive is to understand the serological short-, medium- and long-term immune response in vaccinated people by: i) Determining the baseline immune status of people receiving Covid-19- vaccines and the prevalence of individuals (silently and symptomatic) infected before vaccination, ii) Describe and compare the dynamics of antibody titers of vaccinated individuals over time and in relation to the vaccine received or preexisting immunity, iii) Determine the relative risk of post-immunization infection with COVID-19 (variants) in relation to the antibody titer at the time of infection, iv) Collect data on the perceived COVID-19 status, the individual motivation to be vaccinated, the type of vaccine received, factors that may influence immune response (e.g. immune suppression) and basic demographic data