“Seroprevalence of SARS-CoV-2 antibodies and associated risk factors in children less than 6 years of age in the canton of Fribourg, Switzerland (COVPED study): a population-based cross-sectional study”, Swiss Med Wkly, vol. 152, no. 2122, p. w30173, May 2022, doi: 10.4414/SMW.2022.w30173.