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.

Cases of hMPV are on a steady rise and the pathogen has been identified as a main cause of respiratory illness and hospitalizations this winter, said the Chinese Center for Disease Control and Prevention. While not a new virus, hMPV appears to also be vexing governments across the region, with India, Malaysia and Hong Kong reporting cases in recent days. Indonesia and Vietnam said they are closely monitoring the hMPV situation in China, asking the public not to panic.

The new attention on hMPV — just one among a host of germs that causes the common cold — is likely due to improved virus detection capabilities in China and other countries after the COVID pandemic, during which governments spent millions on testing infrastructure, and companies raced to develop better virus detection kits. And five years after SARS-CoV-2 sent the world into lockdown, outbreaks of illness in China attract outsized attention, and are often the subject of misleading social media posts.

In 2023, pneumonia cases in Chinese children prompted the World Health Organization to ask Beijing to share information about respiratory pathogens in circulation.

HMPV, first discovered in the Netherlands in 2001, has become far easier to detect and is among a suite of respiratory pathogens that common-used testing kits now screen for.

Lab testing for pathogens including hMPV used to take a long time, with results often confirmed long after a patient had already recovered. “Testing these days can identify the virus causing infections within half an hour, so patients will quickly find out and that’ll trigger more learning and attention,” Hu Yang, a physician at Shanghai Pulmonary Hospital, told the National Business Daily last month.

Although hMPV can make people very sick, the current situation is “very different” to the COVID-19 pandemic which was completely new to humans, said Professor Jill Carr, a virologist at Flinders’ University’s College of Medicine and Public Health.

Its symptoms are mild in most cases, include coughing, fever, running nose and sore throat. There is no vaccine for the virus, and it can cause pneumonia or even lead to hospitalization in high-risk groups such as children, elderly with chronic diseases, and patients receiving immunosuppressive treatments.

China will continue to see multiple pathogens fueling its winter illness outbreak through spring, the country’s CDC said in December 2024.