This article was published in Volume 112, issue 4 of publishing year 2021, with a mistake in the text and in Table I. The corrections to the text and the correct Table I are the ones included in this erratum. Page 514, second full paragraph, line 30 should read as follows: "According to Table I, a nasal swab (rapid test) for detection of SARS-CoV-2 specific antigen was performed in 33 countries and in 46 children, respectively, in the treated and in the control groups."