The recent surge in respiratory virus cases in China and Europe has raised concerns about the potential for another pandemic. In China, hospitals in more than three major cities in the northern region have been overwhelmed by the influx of infected patients. Initially referred to as “pneumonia of unknown origin” by Chinese authorities, the cause of the outbreak has now been identified as human metapneumovirus (hMPV).
hMPV, first discovered in 2001, has a history of causing significant outbreaks, including a major one in 2017. During that time, heightened hMPV activity was reported across North America, Europe, and parts of Asia, with genetic analyses revealing variability within its subgroups (A1, A2, B1, B2).
Recent Developments: The 2024-2025 hMPV Variant
The current outbreak, which began in late 2024, is marked by rapid transmission and severe symptoms, including pneumonia. Thousands of hospitalizations have been reported, with one notable instance being Tianjin Children’s Hospital, which recorded over 13,000 young patients in a single day across its outpatient and emergency departments.
While the genetic characteristics of the new hMPV subgroups have not yet been fully investigated, the symptoms and extended disease duration (ranging from 5 days to 3 weeks) suggest that the recent variants could be highly virulent. Notably, hMPV’s RNA-dependent RNA polymerase (RdRp) lacks a genetic proofreading mechanism, making the virus prone to mutations and the emergence of new variants.
Clinical Implications of hMPV Infection
hMPV can cause severe bronchiolitis, bronchitis, and pneumonia, particularly in children and young adults. Its symptoms are often indistinguishable from those caused by respiratory syncytial virus (RSV). Initial infections typically occur in early childhood, but reinfections are common throughout life.
Due to the virus’s slow growth in cell culture, molecular diagnostic methods, such as reverse transcriptase polymerase chain reaction (RT-PCR), are the preferred approach for detecting hMPV.
Key Observations from Recent and Past Outbreaks
Geographical Spread: Reports of heightened hMPV activity have come from North America, Europe, and parts of Asia.
Healthcare Strain: in the US already Hospitals and clinics have experienced a significant increase in respiratory infections, especially among children, the elderly, and immunocompromised individuals.
Coinfections: The outbreak often coincides with other seasonal respiratory viruses, such as influenza, RSV, and non-SARS coronaviruses, complicating diagnosis and management.
Diagnostic Challenges: Coinfections make it difficult to attribute symptoms solely to hMPV, further straining healthcare resources.
