A respiratory virus you've probably never heard of is quietly costing the healthcare system as much as the better-known RSV, according to new research that's raising alarms about the need for better treatments and vaccines. Human metapneumovirus, or hMPV, sends thousands of adults to the hospital each year with similar severity to respiratory syncytial virus (RSV), yet it remains largely overlooked in public health discussions.

What Is Human Metapneumovirus and How Does It Compare to RSV?

A new study published in Open Forum Infectious Diseases examined hospitalization costs for nearly 6,000 adults who tested positive for either hMPV or RSV between July 2011 and July 2024 . Researchers from Kaiser Permanente Southern California analyzed data from 2,810 patients hospitalized with hMPV and 2,965 with RSV, comparing everything from hospital stay length to intensive care unit (ICU) admissions and treatment costs.

The findings reveal striking similarities between the two viruses. Adults hospitalized with hMPV stayed in the hospital for an average of 6.4 days, compared to 6.8 days for RSV patients. Both viruses required ICU admission at similar rates, with 14.8% of hMPV patients and 16.5% of RSV patients needing intensive care. Respiratory support, such as oxygen or ventilation, was needed by roughly one in four patients with either virus .

Why Are Hospitalization Costs So High for Both Viruses?

The adjusted mean hospitalization costs tell a sobering story. Adults hospitalized with hMPV incurred average costs of $20,188, while RSV patients averaged $21,759 . These figures represent a substantial burden on the healthcare system and on families facing unexpected medical bills.

One notable difference emerged in the data: hMPV patients were diagnosed with pneumonia at higher rates than RSV patients, 66.7% versus 56.8% respectively . This complication likely contributes to the overall severity and cost of hMPV hospitalizations. The researchers emphasized that the economic impact of these infections in older adults is considerable, especially as the population ages.

• Hospital Stay Duration: hMPV patients averaged 6.4 days compared to 6.8 days for RSV, showing comparable length of hospitalization
• ICU Admission Rates: About 14.8% of hMPV patients required intensive care versus 16.5% of RSV patients, indicating similar severity
• Respiratory Support Needs: Roughly one in four patients with either virus required oxygen or ventilation support
• Pneumonia Complications: hMPV led to pneumonia diagnosis in 66.7% of cases compared to 56.8% for RSV, suggesting greater lung involvement

Why Should We Care About a Virus Most People Haven't Heard Of?

The research team, which included scientists from drugmaker AstraZeneca, noted a critical gap in medical knowledge. "Although the economic impact of influenza, SARS-CoV-2, and RSV-associated disease in adults has been studied extensively, there are limited data on hMPV-associated healthcare costs in adult populations," the researchers stated . This knowledge gap has meant that hMPV has largely flown under the radar despite causing serious illness.

The timing of this research is significant. As the U.S. population continues to age, the number of older adults vulnerable to severe respiratory infections is growing. Both RSV and hMPV disproportionately affect seniors, who are more likely to develop complications and require hospitalization.

How to Prepare for hMPV and RSV Season

• Know Your Risk Factors: If you're over 65, have chronic lung disease, heart disease, or a weakened immune system, you face higher risk of severe illness from both viruses
• Practice Prevention Basics: Wash your hands frequently, avoid touching your face, and stay home when sick to reduce transmission to vulnerable people around you
• Stay Informed About Vaccines: RSV vaccines are already available for older adults, and hMPV vaccines are in development; talk to your doctor about which options are right for you
• Monitor Symptoms Closely: Seek medical attention if you develop fever, cough, difficulty breathing, or chest pain, especially if you're in a high-risk group

The researchers concluded that the burden of disease from both viruses underscores an urgent need for action. "The increasing proportion of older adults combined with the high cost of hospitalization for hMPV and RSV underscore the importance of the development of vaccines and therapeutics directed against both hMPV and RSV," they wrote . AstraZeneca is already developing an hMPV vaccine, and the company makes Nirsevimab, a monoclonal antibody that protects infants against RSV.

For now, the takeaway is clear: hMPV deserves the same attention and prevention strategies as RSV. Both viruses can cause serious illness in vulnerable populations, both carry substantial healthcare costs, and both warrant investment in preventive measures. As vaccine development continues, staying informed and taking basic precautions remain your best defenses against these silent respiratory threats.