Nature, Published online: 12 March 2025; doi:10.1038/d41586-025-00735-7The immune molecule TGF has been found to weaken immune defences against latent viruses, triggering reactivation of the EpsteinBarr virus. This mechanism links TGF release in SARS-CoV-2 infection to multisystem inflammatory syndrome in children, and could inform the development of therapies for managing this serious condition.