Dr Mattias Larsson* 

Recent reports of a surge in respiratory infections in China have led to concerns of another pandemic. However, the virus responsible for this increase, human metapneumovirus (hMPV), is neither new nor mysterious.

Authorities in both countries have denied claims that their healthcare systems are overwhelmed, emphasising that the situation is under control.

Human metapneumovirus is a common virus that infects the respiratory tract, causing symptoms similar to the common cold -sore throat, runny nose, coughing and sneezing. Nearly everyone is infected with hMPV by age five, and like the flu, reinfections are common as immunity decreases and new variants emerge.

For most people, hMPV causes mild symptoms. However, it can lead to severe illness in vulnerable populations, including young children, the elderly, and those with weakened immune systems or conditions like asthma. Globally, the virus killed at least 11,000 children under the age of five in 2018. For comparison, respiratory syncytial virus (RSV), another cold virus, causes about 60,000 child deaths annually.

hMPV has likely been circulating in humans for centuries. First discovered in 2001 in the Netherlands, it has been found in samples dating back to 1976, and antibodies to the virus were detected in blood samples from the 1950s. The virus is thought to have evolved from avian metapneumoviruses, which affect birds, around 200 years ago.

hMPV belongs to the paramyxovirus family, which includes viruses like measles and Nipah. It has a relatively simple genome of around 13,000 RNA 'letters' and codes for nine proteins. While it primarily infects humans, it can also affect animals, such as chimpanzees and gorillas.

Currently, there are no specific treatments or approved vaccines for hMPV. However, vaccines are in development, including a 2024 mRNA vaccine from the University of Oxford aimed at protecting children from both hMPV and RSV.

Why are there so many cases of hMPV now?

Winter typically brings waves of cold and flu infections, and some years these waves are larger than others. The increased number of infections naturally leads to more severe cases and hospital admissions.

In China, the government has reported a rise in respiratory infections, with hospitals experiencing more admissions. Similarly, in Việt Nam, hMPV infections have been on the rise, particularly affecting young children.

As of early January 2025, local authorities have reported over 1,000 cases of hMPV in HCM City alone, with a significant number of hospitalisations due to complications.

However, both China and Việt Nam's health ministries insist that the situation is manageable and that the infections are following typical seasonal patterns.

Unlike COVID-19, hMPV is not a new virus, and many people already have some immunity to it, especially older children and adults. The variant currently circulating in China and Việt Nam shows only minor mutations from previous strains, and there is no evidence suggesting it will cause a pandemic.

China’s foreign ministry confirmed that while infections have risen, they are less severe and spread on a smaller scale compared to the previous year. Similarly, Việt Nam's health authorities have assured the public that the rise in infections is manageable and not a cause for panic.

While hMPV is causing a seasonal uptick in respiratory infections in China and Việt Nam, it is not a new or exceptionally dangerous health threat. The rise in cases is in line with typical winter epidemic patterns, and the situation does not point to the start of another pandemic. Family Medical Practice

*Dr Mattias Larsson is a paediatric doctor at Family Medical Practice and associate professor at Karolinska Institutet and has a long experience in research on infectious diseases. He has worked with the Oxford University Clinical Research Unit and the Ministry of Health of Vietnam. He is fluent in English, Swedish, Vietnamese, German and some Spanish.

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