P. Bruggmann, O. Senn, A. Frei, M. A. Puhan, J. Fehr, and L. Falcato, “High SARS-CoV-2 seroprevalence but no severe course of COVID-19 disease among people on opioid agonist treatment in Zurich: a cross-sectional study”, Swiss Med Wkly, vol. 152, no. 0102, p. w30122, Jan. 2022.