Human metapneumovirus (HMPV) is a respiratory virus that circulates during cold and flu season, can be severe in young infants and elderly people, and is often mistaken for influenza or respiratory syncytial virus (RSV)—but a new study reveals important clinical differences that could change how doctors diagnose and treat it. What Is Human Metapneumovirus and Why Should You Care? You've probably never heard of human metapneumovirus, but there's a good chance you or someone you know has had it. HMPV was first discovered in 2001, and it circulates every year during the respiratory virus season alongside flu, RSV, and COVID-19. The virus causes acute respiratory illness (ARI)—basically, a respiratory infection that comes on suddenly—and can range from mild to severe depending on your age and health status. The problem is that HMPV often gets confused with other common respiratory viruses, which means people might not get the right care or understanding of what they're dealing with. A recent study published in Open Forum Infectious Diseases analyzed data from five influenza seasons, including both pre-pandemic years (2016-17 to 2019-20) and pandemic years (2021-22), to better understand how HMPV behaves in real-world outpatient settings. The research was conducted at the Pittsburgh site of the Centers for Disease Control and Prevention (CDC)-funded US Flu VE Network study and included patients 6 months and older who came to outpatient clinics in southwestern Pennsylvania with a new or worsening cough lasting less than 7 days. How Common Is HMPV, and When Does It Strike? The study found that HMPV was detected in 4.7% to 7.3% of patients with acute respiratory illness across the five seasons examined. That might not sound like a huge percentage, but when you consider how many people get respiratory infections each year, those numbers add up quickly. What's particularly interesting is the timing: HMPV peaks much later in the season than influenza does. In the 2018-19 and 2021-22 seasons, HMPV activity seemed to peak in April, well after the typical flu season winds down. The West Coast is currently experiencing large clusters of HMPV activity. The San Francisco Chronicle has reported school and work absences in the Bay Area due to the virus, suggesting that HMPV is circulating at significant levels right now. How Does HMPV Compare to Other Respiratory Viruses? One of the most important findings from the study is how HMPV symptoms differ depending on your age. For children ages 5 to 17 years, the symptoms of HMPV and RSV were indistinguishable—meaning doctors can't tell them apart just by looking at symptoms alone. However, adults with HMPV reported feeling worse during follow-up than adults with flu, suggesting that HMPV may cause more severe illness in older populations. This distinction matters because it affects how doctors approach treatment and monitoring. Unlike RSV, flu, and COVID-19—all of which now have vaccines available—there is currently no vaccine for HMPV. The virus can cause severe illness and outbreaks, which is why understanding its clinical characteristics has become increasingly important. Why the Lack of a Vaccine Is a Problem The absence of an HMPV vaccine is a significant gap in our respiratory virus defenses. We now have vaccines that can help prevent infection from RSV, influenza, and COVID-19, but HMPV remains unprotected. This means that prevention relies entirely on standard infection control measures like hand hygiene, respiratory etiquette, and staying home when sick. For vulnerable populations—particularly young infants and elderly people—this lack of vaccine protection is concerning, especially given that the virus can cause severe disease in these groups. Steps to Protect Yourself From HMPV and Other Respiratory Viruses - Practice Hand Hygiene: Wash your hands frequently with soap and water for at least 20 seconds, especially after being in public spaces, before eating, and after coughing or sneezing. Hand sanitizer with at least 60% alcohol can work if soap and water aren't available. - Cover Your Cough and Sneeze: Use a tissue or the inside of your elbow to cover your mouth and nose when you cough or sneeze, then dispose of tissues immediately and wash your hands. This prevents respiratory droplets from spreading to others. - Stay Home When Sick: If you have respiratory symptoms like a cough, fever, or congestion, stay home for at least a few days to avoid spreading the virus to vulnerable people, especially infants and elderly individuals. - Get Vaccinated Against Available Viruses: Make sure you're up to date on flu, RSV, and COVID-19 vaccines, which can reduce your risk of severe illness from those viruses and help protect those around you. - Maintain Distance During Peak Seasons: During respiratory virus season (typically fall and winter, with HMPV peaking in spring), try to maintain distance from people who are sick and avoid large crowds if you're in a high-risk group. What Should Doctors Be Looking For? The clinical understanding of HMPV is becoming increasingly important now that RSV, flu, and COVID-19 have vaccines available. Doctors need to be able to distinguish HMPV from these other viruses so they can provide appropriate counseling and monitoring. The study's findings suggest that in children, additional testing may be needed to differentiate HMPV from RSV since their symptoms are so similar. In adults, the fact that HMPV causes more severe symptoms than flu might prompt doctors to take the illness more seriously and monitor patients more closely. The emergence of HMPV as a notable respiratory pathogen—especially with current activity clusters on the West Coast—underscores the importance of staying informed about lesser-known viruses that can still cause significant illness. While HMPV may not get the headlines that COVID-19 or flu do, it's a virus worth knowing about, particularly if you're caring for young children or elderly family members.
