Another similarity to COVID: A case of HMPV can last about a week, with symptoms peaking around the third day, Dr. Hoy told us. However, you can still be contagious for several days after you're feeling better and your symptoms subside. This is especially the case for patients with compromised or weakened immune systems.

A virus that's not well known to the public is spiking in China. CDC officials said HMPV is not a cause for concern here, nor is it a new virus.

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.