While cases are climbing in China, the situation is very different from what it was when Covid-19 emerged five years ago, medical experts say. HMPV has circulated in humans for decades.

In China, reports of HMPV infections have indeed been rising in recent weeks in the more northerly regions. But so have reports of all the other respiratory pathogens including seasonal flu, rhinovirus and RSV.

As cases of the HMPV virus continue to increase in the U.S. and in China, here's what you need to know about the virus.