Seroepidemiological studies have been of great interest since the onset of the Coronavirus Disease 19 (COVID-19) pandemic, as they provide information on the percentage of the population that has already experienced a Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection, including unrecognized infections (under-reporting). This can help to better assess the course and dynamics of the pandemic and to improve response planning. (Epid Bull 37/2021)