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 is common and decades old.

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.