"Untangling such interference hasn’t been easy given the number of respiratory viruses—coronaviruses, rhinoviruses, adenoviruses, RSV, and influenza are just among the best known—and the many infections that escape notice. Recent advances in technology, however, make it easier to detect infections in people and study how multiple viruses behave in the lab, in cell cultures or stem cell–derived tissues known as organoids. Increasingly, researchers are fingering a cause: chemical messengers that infected people produce called, fittingly, interferons."