Long COVID made the idea familiar, but new evidence indicates that influenza and respiratory syncytial virus can also leave people unwell for months, with lung problems after flu and heart events after RSV showing up most consistently.
A systematic review published in the journal Respirology pulled together 13 observational studies covering 631,863 people and spanning January 2004 through August 2025. The work was led by a team from Duke-NUS Medical School in Singapore.