As China continues to monitor an increase in cases of human metapneumovirus (HMPV), here's what you need to know about the illness.

As China experiences a rise in respiratory infections this winter, one little-known virus has gotten a lot of attention – and some people may worry whether the rise in cases could be felt more broadly around the world.

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.