Correction to: Nature Medicine https://doi.org/10.1038/s41591-020-1001-6, published online 14 July 2020.

In the version of this article initially published, two values in the final two sentences of the first paragraph of the ‘Interventions’ subsection of the Methods section ("...risk of transmission would be decreased by 53% if all individuals were wearing masks....both measures would reduce risk multiplicatively by 67%...”) were incorrect. The correct text is as follows: "...risk of transmission would be decreased by 47% if all individuals were wearing masks....both measures would reduce risk multiplicatively by 63%...". Also, four values in the ‘Efficacy of masks’ section of Supplementary Table 3 (top group, “If efficacy is fixed at 79% (instead of 53% in the main analysis)”; second group, “If efficacy is fixed at 36% (instead of 53% in the main analysis)”) were incorrect. The correct values are as follows: “If efficacy is fixed at 64% (instead of 47% in the main analysis)” (top group); and “If efficacy is fixed at 21% (instead of 47% in the main analysis)” (second group). Finally, three values in the first sentence of the legend to Extended Data Fig. 4 (“...at 36% a, c, e, and 79% b, d, f, instead of 53%...”) were incorrect. The correct values are as follows: “...at 21% a, c, e, and 64% b, d, f, instead of 47%...”. The errors have been corrected in the HTML and PDF versions of the article.