HMPV cases surge in the US: The “unknown virus” fueling global fears

The human metapneumovirus (HMPV), a little-known respiratory illness, has sickened nearly 28,000 Americans over the past year, according to federal data.

Often dubbed “the most important virus you’ve never heard of,” HMPV is contributing to pandemic fears in China and raising alarms in the U.S., though it remains overshadowed by other winter illnesses like flu, RSV, and Covid-19.

Spike in HMPV Cases Across the U.S.

Infections peaked in April 2024, with one week reporting 1,666 positive cases—8% of all tests conducted that week. While current numbers are lower, the CDC recorded 260 positive tests for the week ending December 28, reflecting a 1.9% positivity rate. Since Thanksgiving, weekly cases have ranged from 200 to 350, a level health officials say is typical.

HMPV, first identified in 2001, usually causes mild cold-like symptoms such as cough, fever, and runny nose. However, severe cases can lead to bronchitis, bronchiolitis, or pneumonia, especially in vulnerable populations. Approximately 20,000 U.S. children under age five are hospitalized with HMPV each year, and the virus has an estimated fatality rate of 10-30% among hospitalized patients.

Midwest States See Surging HMPV Rates

Certain regions are seeing disproportionately high rates. In the Midwest, including Missouri, Kansas, Nebraska, and Iowa (Region 7), HMPV positivity rates are triple the national average. By contrast, northeastern states like Maine, New York, and Massachusetts (Regions 1 and 2) recorded positivity rates of just 0.9% for the week ending December 28.

Comparison to Other Respiratory Illnesses

Despite its impact, HMPV remains far less prevalent than other respiratory illnesses. Since October, over 9.3 million Americans have been infected with influenza, 4.9 million with Covid-19, and 1.2 million have visited doctors for RSV-related symptoms. The CDC estimates these illnesses have led to tens of thousands of hospitalizations and deaths.

For the week ending December 28, flu accounted for 5.2% of hospital visits—a dramatic rise from just 1% a month earlier. RSV accounted for 1%, while Covid-19 visits stood at 1.2%. Hospitalizations for all three illnesses also increased, with flu hospitalizations reaching 4%, while Covid-19 and RSV each accounted for 2%.

Pandemic Fears in China

In China, hospitals in northern provinces are reportedly overwhelmed by a viral outbreak linked to HMPV and other respiratory illnesses. One in three flu tests in China returned positive between December 29 and January 5, totaling nearly 7,000 new cases. While flu rates show signs of slowing, other respiratory illnesses, including HMPV, continue to spike.

Transmission and Prevention

Like Covid-19, HMPV spreads through respiratory droplets from coughing or sneezing, as well as through close personal contact or touching contaminated surfaces. There are currently no vaccines or specific treatments for HMPV, making prevention through masking, handwashing, and social distancing crucial during outbreaks.

Looking Ahead

With winter illnesses surging in both the U.S. and China, health officials remain on high alert. While HMPV has yet to reach the scale of influenza or Covid-19, its potential for severe illness in vulnerable populations underscores the importance of monitoring and prevention. As respiratory viruses continue to rise, experts urge vigilance to limit their spread and mitigate their impact.