Human metapneumovirus is finally being taken seriously

Like many other respiratory viruses, Williams says hMPV tends to affect those with chronic lung disease or pre-existing conditions such as asthma and cancer. But even so, he found, many doctors don’t know it’s a threat, in large part because until relatively recently, no one was testing it outside of academic research.

“There’s no doubt that even in the medical community, many doctors are simply not aware of how common hMPV is,” he says. “As clinical tests have become more available, I’ve had people say to me with surprise, ‘I had a patient in the ICU with metapneumovirus last week. It’s real and I never believed it before. Until people see it for themselves, I think they don’t fully believe the gravity.

Vermund says there have probably been many spikes of hMPV infections in the past, but we either didn’t know about them or mistook them for the flu. He explains that one of the consequences of Covid is the recognition of the need for greater surveillance of circulating respiratory viruses, which means that the number of hMPV cases is being detected by epidemiologists for the first time.

“The Chinese are quite advanced in molecular diagnostics for respiratory viruses and do a lot of public health surveillance, more than many other countries,” he says. “I think what we may be seeing is that they’re doing a particularly good job at that, and so finding that metapneumovirus is more common than we used to realize.”

Williams believes the current surge in interest in hMPV could have positive public health implications. Currently, he says, hMPV can only be detected as part of a so-called multiplex panel, a diagnostic that checks for the presence of up to 25 different respiratory viruses, at a cost of about $200 per patient. While this is a worthwhile investment for emergency room doctors deciding whether to admit a sick baby or send him home, such costs are often prohibitive for ordinary doctors.

“There are low-cost tests for influenza, Covid and RSV that can be used by clinicians everywhere,” he says. “But there’s really no cheap test for hMPV, just this complex diagnostic panel that evaluates multiple viruses, and it’s hard for the average clinic to get hold of.”

There are hopes that low-cost testing for hMPV may be on the way. According to Vermund, the Ragon Institute in Massachusetts is working on ways to try to lower the cost of testing for respiratory viruses to under $6 per patient, with the ultimate goal of bringing the cost down to less than $1.

Also, another consequence of the growing awareness surrounding hMPV is that it provides stronger incentives to fast-track a vaccine. No licensed vaccine for the virus is yet available, but a series of candidates have emerged early stage clinical trials in the last two years.

Last summer, scientists from the University of Oxford started a clinical trial of a combination vaccine against RSV and hMPV in partnership with Moderna, and Andrew Pollard, professor of infection and immunity who leads the Oxford Vaccine Group, says adding hMPV to existing vaccines would be the most practical way to introduce additional immunization.

“If you can put them in the same vaccine, RSV and hMPV, then without needing extra needles, you’re actually covering more of the respiratory hospital admissions,” says Pollard. “But before we can do that, we need to understand how often you should get vaccinated against hMPV.” If you can provide immunity by vaccinating every few years, then you can combine with RSV.

Overall, Vermund describes the sudden interest in hMPV as an important development. Although the virus will not cause the next pandemic, it still affects such a significant number of people that it is a major drain on public health systems, as well as a long-unrecognized cause of death among the vulnerable.

“Although metapneumovirus is not one of the deadliest viruses, it is incredibly common,” he says. “It causes a non-trivial amount of colds over the years, which is an incredible economic burden, and occasionally kills someone.”