What Is Human Metapneumovirus, and Why Are Cases Rising in China?

HMPV Cases Are Rising Across Asia, but Experts Say Not to Panic

By Lauren J. Young edited by Dean Visser

Cases of a common respiratory virus called human metapneumovirus, or HMPV, are surging in several Asian countries, but experts say the situation shouldn’t trigger fears of a larger global health threat. HMPV falls into the same mix of winter bugs as influenza and respiratory syncytial virus (RSV), which often peak during this time of year in the Northern Hemisphere. Common HMPV symptoms, such as a runny nose, coughing and fever, are typically mild. Young children, older adults and people who are immunocompromised may be at a higher risk of severe disease, however.

In mid-December 2024 health agencies in China reported an overall increase in respiratory infections, including an HMPV uptick in children under 14 years old in northern China. Reports of a hospital allegedly flooded with cases further fueled alarm and attention to this lesser known yet common winter respiratory disease.

“In Asia, they are having a fairly large outbreak—might even call it an epidemic—of human metapneumovirus,” says William Schaffner, an infectious disease physician and a professor at Vanderbilt University Medical Center. “There’s no need to be panicky. But for those folks who are in higher-risk groups, this is a time to be careful, [to] be cautious.”

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China’s relatively large case count has prompted the nation and nearby countries to increase surveillance. Cases have also been detected in Malaysia, India and Kazakhstan. Experts note that HMPV has been occurring in humans around the world for decades, however.

“The virus has circulated for at least 60 years, and genetic evolutionary studies suggest that it diverged from a bird virus between 200 to 400 years ago,” says John Williams, a pediatrician and infectious diseases professor at the University of Wisconsin–Madison, who has studied HMPV for more than 20 years. “HMPV causes regular annual seasonal epidemics, similar to the more widely recognized influenza virus and RSV. The typical HMPV season is late winter to early spring. So this isn’t totally unexpected.”

Williams says widespread population immunity should lower the risk of a larger public health problem. Schaffner adds that it’s plausible that travelers in countries with high HMPV rates could “bring the virus to the U.S.—but it’s here already.”

The U.S. experiences seasonal spikes annually. The U.S. Centers for Disease Control and Prevention currently reports a slight uptick in HMPV in the country. Cases are still low, however: as of the week of December 28, nearly 2 percent of diagnostic tests were positive for the virus. Last year HMPV peaked in April with about 8 percent of tests coming back positive.

Scientific American spoke further with Schaffner about the recent HMPV outbreaks, common symptoms and those who are most vulnerable to severe disease.

[An edited transcript of the interview follows.]

What is HMPV?

Human metapneumovirus is another one of those winter respiratory viruses in the same family as RSV, and it increases during this time of the year [in the Northern Hemisphere]. The virus affects our nose, throat and chest, so it’s readily transmissible person-to-person. Researchers have been looking at this virus for some time, but because it doesn’t have the prominence of influenza and COVID, for example, it hasn’t been as well known to either the medical community or the general public. It’s also less well known because we haven’t had easy and more widely available diagnostics. But now patients who are hospitalized, and even patients who are seen in doctors’ offices, can receive rather quick diagnostic tests. So doctors are making this diagnosis more frequently than they used to. This virus has come to more attention, but it’s always been there.

What are the symptoms?

Like other respiratory viruses, it can cause a stuffy nose, a sore throat or a cough because it goes down into your bronchial tubes. Some people can get complications of pneumonia. We are most concerned about young children because they haven’t had experience with or immunity to the virus, older, frail people who have chronic underlying illnesses and people who are immunocompromised.

What do we know so far about the recent outbreaks and cases?

In Asia, they are having a fairly large outbreak—might even call it an epidemic—of human metapneumovirus. It’s being diagnosed here in the U.S. But at the moment, influenza, COVID and RSV are much more prominently recognized at present. We’re able to make these diagnoses much better, and so the harder we look, the more we’ll find. I don’t think this is something we should be alarmed about. It’s certainly nothing nefarious. And yes, some of those travelers [to countries with higher rates of HMPV] could bring the virus to the U.S.—but it’s here already. I’m more concerned for the U.S. population now with influenza, which has rocketed up over the past several weeks, and our hospitals and emergency rooms are just chock-full of people who are really miserable and quite sick with influenza. And COVID and RSV are increasing also at the present time.

Is there any concern for a larger global outbreak or pandemic?

I don’t think we can call it a pandemic because there’s nothing new about this virus. Different parts of the world can increase at different times, but we are a global village, as the saying goes. And obviously these viruses don’t need passports, so all of them can move around the world and be introduced just through the way human beings travel. And there’s been an awful lot of internal travel here in the U.S. over the holiday season; many people getting together, family reunions, parties and the like. That’s provided an environment for all of these respiratory viruses to accelerate their spread.

How can you minimize risk of HMPV infection?

We don’t have a vaccine against the human metapneumovirus, so what we can do is avoid people who are coughing and sneezing. If you become ill, please don’t go to school or work. Stay home. If you’re coughing and sneezing, do that in your elbow. If you’re going to an indoor place where there are a lot of other people, wear your mask. If you’re really in that high-risk group, think about some social distancing. Let’s wait until these viruses pass, and then we can go out and about. So social distancing and wearing the mask really do help, along with good hand hygiene at all times.