Metapneumovirus (hMPV) – Is a New Pandemic Emerging from China?

What Is hMPV?

Human metapneumovirus (hMPV) is a single-stranded RNA respiratory virus belonging to the Pneumoviridae family. It usually causes mild upper respiratory infections with symptoms such as cough, fever, nasal congestion, and sore throat, but it can cause bronchiolitis and pneumonia, particularly in infants, older adults, and people with weakened immune systems. The virus is transmitted through droplets and can spread through contact with contaminated surfaces.

hMPV was first identified in the Netherlands in 2001 by van den Hoogen and his team. The researchers identified this new virus by isolating it in children who had respiratory infections but were found not to be infected with known pathogens.

Why Is hMPV in the News?

Since the COVID-19 pandemic swept across the world in 2020, awareness of infections caused by respiratory viruses has increased globally. Most recently, the China Center for Disease Control and Prevention's December 2024 report of a marked rise in respiratory infections, a substantial proportion of which were human metapneumovirus (hMPV) cases, drew attention to this virus. Could this situation signal a new pandemic? Let us look at the experts' views.

What You Need to Know About hMPV: Questions and Answers

1. What Is hMPV and How Does It Spread?

• Answer: hMPV is a negative-sense, single-stranded RNA virus belonging to the Pneumoviridae family. It was identified in the Netherlands in 2001 and is particularly closely related to avian metapneumovirus (subgroup C).

• The virus usually spreads through direct contact with infected people's respiratory secretions or by touching contaminated surfaces.

2. What Are the Symptoms and Who Is at Risk?

• Answer: hMPV usually presents as an upper respiratory infection. Common symptoms include cough, fever, nasal congestion, and sore throat . Most cases are mild and resolve within 2-5 days. However, infants younger than 12 months, older adults, and immunodeficient patients , as well as people with hypertension, diabetes, obesity, cancer, cardiovascular disease, and chronic respiratory diseases , may develop serious symptoms such as bronchiolitis and pneumonia.

Information for cancer patients:

• Cancer treatment (chemotherapy, radiotherapy, immunotherapy) weakens the immune system and may leave patients vulnerable to infections.
• hMPV infection may cause more serious respiratory complications, particularly in patients with lung cancer.
• People receiving treatment for blood disorders such as lymphoma and leukemia become more susceptible to respiratory infections because of immunosuppression.

Recommendation: It is important for cancer patients to take signs of infection seriously and consult their doctors even when symptoms are mild. Prompt intervention may be needed, particularly for high fever, shortness of breath, or severe fatigue.

3. Why Did the Cases in China Attract So Much Attention?

• Answer: Images of crowded hospitals and rising case numbers shared on social media sparked fears of an approaching pandemic. However, experts note that hMPV has a seasonal pattern similar to influenza and that cases usually increase in winter.

4. What Is "Immune Debt" and How Is It Related to hMPV?

• Answer: Because of the strict restrictions imposed during the COVID-19 pandemic, many respiratory viruses, including hMPV, did not circulate for 2 years. This reduced immunity in the general population and resulted in groups of hMPV-naive children who had never encountered the virus.

• Experts call this phenomenon "immune debt," and it led to a resurgence of hMPV cases.

5. What Do hMPV's Genetic Evolution and Mutations Mean?

• Answer: RNA viruses tend to mutate, which may lead to the emergence of new subtypes. Recently, hMPV variants containing 111- and 180-nucleotide duplications in the G gene have been identified.

• Although these genetic changes add new amino acids to the virus's outer envelope proteins, creating a different antigenic surface, they do not increase disease severity.

6. Is There a Risk in Turkey?

• Answer: Although human metapneumovirus (hMPV) cases are seen occasionally in Turkey, available information indicates that no unusual increase or outbreak caused by hMPV has been reported in Turkey. Infectious diseases specialist Prof. Dr. Mehmet Ceyhan has stated that hMPV is regularly monitored in Turkey and usually ranks third or fourth. He has also said that hMPV has no outbreak potential.

7. Is There a Risk in Europe?

• Answer: The European Centre for Disease Prevention and Control (ECDC) stated that the cases in China reflect an expected seasonal increase in respiratory infections overall and currently pose no significant threat to Europe.

• Observations show that, in Europe, acute respiratory infections increase every winter and that current hMPV circulation is at the expected level.

8. Is There a Vaccine or Treatment for hMPV?

• Answer: There is no vaccine or specific antiviral treatment for hMPV. However, symptomatic treatment can reduce patients' discomfort. Supportive treatment is recommended for immunocompromised people and at-risk groups.

Conclusion

In light of the available data, experts state that hMPV is unlikely to pose a threat similar to the COVID-19 pandemic. However, to protect public health, they recommend hygiene measures, mask use for at-risk groups, and avoiding crowded settings. Respiratory infection cases in different countries, particularly China, should be closely monitored to develop policy recommendations based on epidemiological data.