Correction to: Nature Reviews Immunology https://doi.org/10.1038/s41577-024-00992-z, published online 18 January 2024.

The originally published article contained several errors that have now been corrected. One trial of BCG vaccination reported a large beneficial effect, and a sentence describing the trials has been changed to reflect this; “small” has been removed from the sentence “three reported a beneficial effect on BCG vaccination.” A description of one trial had not included the number of case participants and this has been amended to now read “with COVID-19 occurring in 1 of the 96 participants in the BCG group compared with 6 of the 48 in the control group.” In the “What have we learnt?” section, two of the original references were mixed up and have now been corrected: “…the definition of the primary outcome in only one of these” now cites reference 12, and “In the other two trials…” now cites references 10 and 13. The authors apologise for these errors, which have now been corrected in the HTML and PDF versions of the article.