Mysterious HMPV Virus Surges Across U.S., No Vaccine in Sight

Human metapneumovirus (HMPV), a virus discovered in 2001 and related to RSV, is driving a sharp rise in respiratory illnesses across multiple U.S. states, with Northern California hit hardest since mid-February 2026. Wastewater surveillance from Waste Water Scan shows surges in the Northeast as well, marking higher activity than most prior seasons except 2022-2023. In California, test positivity reached 8.6% for the week ending February 28, per voluntary lab data to the California Department of Public Health.[1][2] HMPV mimics common colds, flu, COVID-19 and RSV, evading standard nasal swabs and requiring separate emergency room tests for confirmation, said Dr. William Schaffner, Vanderbilt University preventive medicine professor. Young children, older adults and those with weakened immune systems face the greatest risk of severe symptoms like breathing difficulties, high fever, dehydration and pneumonia, particularly smokers or people with asthma.[1][6] At UC San Francisco, Dr. Peter Chin-Hong reports 10 HMPV cases weekly—double last month's rate—with one to two severe cases needing oxygen, IV fluids or ventilators. "We don’t have therapy for HMPV but identifying it helps predict outcomes," Chin-Hong said. The virus lacks a vaccine or antiviral, leaving supportive care as the only option.[1] CDC data as of March 27, 2026, shows low overall acute respiratory illness but notes delayed RSV peaks potentially extending into April, alongside declining flu and low COVID-19. HMPV, while not nationally reportable everywhere, aligns with NREVSS and wastewater trends spiking in Sacramento, Davis, Vallejo and San Francisco.[2][3] Separate from HMPV, CDC monitors rising Mycoplasma pneumoniae bacterial infections since late spring 2025, peaking in August among young children, with 2 million annual U.S. cases estimated but no dedicated tracking.[4][5] Experts urge vigilance as HMPV circulates late into spring.