What is HMPV?

HMPV is a respiratory virus similar to respiratory syncytial virus (RSV). Although HMPV was first identified in 2001, researchers say it has circulated in humans for at least 60 years.

"It's oftentimes indistinguishable from the other respiratory viruses, because we don't usually check for it unless somebody is really ill," said Peter Chin-Hong, a professor of medicine and an infectious diseases specialist at the University of California, San Francisco.

Some symptoms of HMPV include cough, fever, sore throat, nasal congestion, and shortness of breath. 

While most cases of HMPV are mild, it can lead to bronchitis and pneumonia in severe cases, particularly in young children, older adults, and those with weakened immune systems.

Currently, cases of HMPV are surging in China, especially in the country's northern region. According to data from China, rates of HMPV, including both outpatient and emergency cases, have been increasing in the country since mid-December.

Although there have been some concerns about a potential health crisis involving HMPV, Chinese authorities have said that the virus is a known pathogen and not a major concern. And while rates of respiratory viruses are currently increasing in the country, a spokesperson for China's Foreign Ministry said that the viruses "appear to be less severe and spread on a smaller scale compared with the year before."

Similarly, the World Health Organization (WHO) has not expressed any concerns about the rise in HMPV cases in China, saying that the increase is expected during the respiratory virus season. "As expected for this time of year, the Northern Hemisphere winter, there is a month-over-month increase of acute respiratory infections, including seasonal influenza, R.S.V. and human metapneumovirus," said Margaret Harris, a WHO spokesperson.

"China is experiencing a large outbreak of human metapneumovirus (HMPV) cases at the moment. Although this is a priority for China's health system, it should not lead to immediate concerns about a new pandemic," said Sanjaya Senanayake, a specialist in infectious diseases at the Australian National University.

Currently, there is no vaccine to prevent HMPV, but common prevention methods include practicing good hand hygiene, covering your nose and mouth when coughing or sneezing, and staying home if you're sick.

Health experts also say that it's important to be vaccinated against other respiratory diseases, such as COVID-19, flu, and RSV, to reduce the risk of coinfection.

"Sure, you can get serious disease from HMPV itself, but if you get HMPV plus pneumococcus or HMPV plus influenza or RSV, it could be much worse," Chin-Hong said. "During respiratory virus season, you want to minimize the probability of co-infection."