As of 15 December 2020, more than 73 million people have been infected with SARS-CoV-2 and over 1.6 million deaths have been reported worldwide (Worldometer, 2021). Viral RNA can remain detectable for more than 100 days in 6.6% of patients after clinical recovery from initial infection; 5% their close contacts develop IgG antibodies, suggesting past exposure (Chirathaworn et al., 2020). Asymptomatic people are also well-documented transmitters of infection. Seropositivity for SARS-CoV-2 among healthcare workers varies between 3%–17% (Chen et al., 2020; Fusco et al., 2020).
