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.

China’s winter illness season is less severe compared to the year before, according to data from its health authority. But the proliferation of a long-standing though little-known pathogen called human metapneumovirus (hMPV) has been raising alarm both at home and in other countries.

Plenty of viruses are having their strongest season for years. But experts have urged calm about HMPV, which is not a new disease — even if you've never heard about it.