Nat. Immunol. 17, 204–213 (2016); published online 4 Jan 2016; corrected after print 17 March 2016

In the version of this article initially published, the affiliation for author Maria Zambon (Health Protection Agency, Porton Down, Salisbury, UK) was incorrect. The correct affiliation should be 'Public Health England, Colindale, London, UK'. The error has been corrected in the HTML and PDF versions of the article.