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HMPV: The Little-Known Virus That Can Be Just as Bad as RSV

Vaccines are under study, but experts say they won’t be available anytime soon

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Older adults are hearing a lot right now about respiratory syncytial virus (RSV), because two new vaccines for the infection are available. But a related virus called human metapneumovirus (HMPV) gets much less attention.

One reason: Though researchers are working on HMPV vaccines, none are about to show up in your local drugstore or doctor’s office.

HMPV causes nothing worse than colds in most people, but it merits attention because of the severe complications it sometimes causes in vulnerable people, says Edward Walsh, M.D., a professor of medicine at the University of Rochester. Though less common than RSV, “in terms of severity, metapneumovirus is every bit as bad,” and “can be really devastating” for some people, he says.

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HMPV did grab some headlines earlier this year when the Centers for Disease and Control and Prevention (CDC) reported a spike in cases. More people than usual tested positive for the virus in the late winter and early spring months in which it typically circulates, the CDC said.

Here’s what you need to know about the virus.

What is HMPV?

Human metapneumovirus, in the same viral family as RSV, is one of many viruses that can cause upper respiratory infections — better known as colds. But the real concern is that it can get deeper into airways and cause pneumonia, says William Schaffner, M.D., a professor of preventive medicine and infectious disease at Vanderbilt University School of Medicine and past medical director of the National Foundation for Infectious Diseases.

In a study by Walsh and colleagues, 2 percent of adults hospitalized with HMPV died, as did 1.6 percent of those with flu and 2.5 percent of those with RSV.

HMPV was first identified by researchers in 2001 but has circulated in people since at least the 1950s, according to a report published in the journal Viruses. The virus is so common that almost all children are infected by age 5; but because immunity wanes, people can get HMPV infections throughout life, the report said. 

Who is most at risk?

Among children, the greatest risks are for babies from about six to 12 months old, Walsh says. After infancy, the greatest risks are in older adults, people with impaired immunity and people with heart or lung conditions such as congestive heart failure, emphysema and asthma, Walsh says.

As with other respiratory viruses, risk rises gradually with age, partly because older people tend to have more underlying health problems, Schaffner says.  “People aged 70 are at greater risk than people at 65,” and the risk keeps rising, he says.


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Can it be prevented?

There’s high interest in vaccines for HMPV, Walsh says, but studies are in the early phases.

A company called Icosavax recently announced promising early results from a clinical trial of a vaccine for both RSV and HMPV in older adults. A second phase of testing just got underway, with initial results expected in 2024, the company said in a press release. Results from a third and larger trial of safety and effectiveness would typically be needed before the company could seek approval from the Food and Drug Administration. Vaccine-maker Moderna also is developing combination vaccines for older adults and children that include HMPV, according to a company press release.

For now, the best way to prevent HMPV is by frequently washing your hands and keeping away from anyone with cold symptoms, Walsh says. And HMPV is just one reason people at high risk for respiratory infections might want to return to masking and avoiding indoor crowds as high season for colds, flus, COVID-19 and other illnesses gets underway, Schaffner says.

It's also important for sick people to keep their distance from those at high risk, Walsh says. “They may think, ‘Oh, I’ve just got a cold. Don't worry about it. It's not COVID And it's not flu,’” he says. “That may be, but you could still create some real havoc.”

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What are the symptoms? 

Unlike the flu, the symptoms of a bad case of HMPV tend to come on gradually, Walsh says: “Typically you start with a little runny nose and a scratchy throat and you think what you’ve got is a little cold,” he says. Often, he says, there’s no fever. “Three or four days later, you may feel just awful,” he says. “You’ll be having a lot of mucus and a lot of cough and a lot of shortness of breath and wheezing and then you end up going to your doctor.”

How is it diagnosed?

You can’t be sure you have HMPV by symptoms alone. And if you go to your doctor’s office, you are unlikely to get tested immediately for HMPV, Shaffner says. People at high risk for complications are likely to get tested for flu and COVID-19 first, he says. That’s because providers can offer targeted antiviral medicine for flu and COVID that work best in the first few days of infection. There’s no such treatment for HMPV.

If you get sick enough to land in a hospital, you are more likely to get tested for a wide range of possible culprits, including HMPV, Shaffner says.

How is it treated?

Treatment focuses on symptom relief. Over-the-counter pain and fever relievers and decongestants are enough for many people, according to the American Lung Association. People with more severe symptoms might need inhaled or oral corticosteroids, the group says. In a study by Walsh and colleagues, people hospitalized with HMPV were at least as likely as those hospitalized with RSV and flu to need additional interventions, including oxygen treatments and intensive care.

Why did cases recently spike?

There are two likely explanations, Shaffner and Walsh agree. One is that HMPV, like many other viruses, was in sharp decline when many people were wearing masks, avoiding crowds and traveling less to avoid COVID-19. Once precautions waned, all sorts of viruses surged back in a less immune population.

The other explanation: more testing. Tests that cover multiple viruses, including HMPV, are used more widely than in the past, especially in hospitals, the experts say. “If you’d been testing for it in the past, you would have found it,” Walsh says.

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