Everything you need to know about human metapneumovirus (HMPV)

Rumours of school closures in the Chinese city of Wuhan, and Beijing's acknowledgement of a surge in cases of human metapneumovirus (HMPV), have prompted understandable concern. Yet, while some people have drawn comparisons with the early days of COVID-19, human metapneumovirus is not a new virus, and is unlikely to trigger the next pandemic.

Human metapneumovirus was first discovered in 2001 by Dutch virologists who were seeking an explanation for various individual respiratory infections that had occurred in recent decades, but which couldn't be attributed to any known pathogen. When they analysed nasal swabs from 28 children who had experienced such infections over the past 20 years, they isolated a previously undiscovered paramyxovirus - a large family of viruses that also includes respiratory syncytial virus (RSV), human parainfluenza, measles and mumps.

"Whilst HMPV does mutate and change over time with new strains emerging, it is not a virus that we consider to have pandemic potential."

- Dr Andrew Catchpole, virologist

Respiratory virus

The virus, which they named human metapneumovirus, caused similar symptoms to RSV, ranging from mild respiratory problems to a severe cough, bronchiolitis (where the small airways of the lungs become inflamed), and pneumonia. Often, patients also suffered a high fever, muscle pain and vomiting. In a pattern that echoes RSV, "very young HMPV-infected children appeared to require hospitalisation and mechanical ventilation," the researchers said.

Having identified this virus, they tested blood samples from other Dutch children, including historic samples. Their investigations revealed that almost all these children possessed antibodies against HMPV by the age of five - a sign of previous exposure - and evidence that the virus had been circulating in humans for at least 50 years.

Subsequent studies confirmed that human metapneumovirus is a common respiratory virus that circulates in many countries during winter and spring. People of all ages can be infected, and reinfected throughout their lives, and while some people who catch it end up in hospital with bronchitis or pneumonia, most experience cold or flu-like symptoms - including a cough, fever, nasal congestion, and shortness of breath - and recover after a few days. Young children, older adults and people with weakened immune systems are at greatest risk of severe illness.

China cases

According to data published by the Chinese Center for Disease Control and Prevention, which tracked health data up until 29 December 2024, there was a continuous upwards trend in respiratory viral infections, including seasonal influenza, rhinovirus, RSV and human metapneumovirus in the final weeks of the year, particularly in northern provinces of China.

"The observed increase in respiratory pathogen detections is within the range expected for this time of year during the Northern hemisphere winter," the World Health Organization (WHO) said. "WHO is in contact with Chinese health officials and has not received any reports of unusual outbreak patterns.

"Chinese authorities report that the health care system is not overwhelmed and there have been no emergency declarations or responses triggered."

Some other temperate northern hemisphere countries have also reported increases in influenza-like illness and/or acute respiratory infections in recent weeks, following usual seasonal trends.

Although more information on the specific strain that is circulating in China would be helpful, "there is no evidence so far that what's being seen in China is much different from what's being seen in Europe. It seems that it is the summation of several common winter viral infections, rather than a new or unknown virus," said Professor Peter Openshaw, a respiratory physician and immunologist based at Imperial College London, UK.

Low pandemic potential

A key difference from the SARS-CoV-2 virus that caused the COVID-19 pandemic is that human metapneumovirus has existed for decades, and most people will have some pre-existing immunity to it.

"Whilst HMPV does mutate and change over time with new strains emerging, it is not a virus that we consider to have pandemic potential. This is because the changes in HMPV are gradual and based on previously circulating strains," said Dr Andrew Catchpole, a virologist and chief scientific officer at hVIVO, a British research organisation that conducts human challenge trials of infectious and respiratory disease vaccines.

"Pandemics occur when a totally new virus enters the human population, like for COVID-19, or in the case of influenza, when a totally new variant of the virus enters the human population by combination [of a human and animal] version of the virus from what is known as the animal reservoir. There is no such animal reservoir of related viruses known for HMPV."

Preventing infection

Even though the risk of a metapneumovirus pandemic is remote, the virus can cause serious disease in some people, and unpleasant symptoms in many others. With no vaccine available to prevent human metapneumovirus or specific antiviral drug to treat it, the best strategy is to try and avoid catching it. Since the virus is thought to spread through coughing and sneezing, or touching objects, surfaces, or hands that have viruses on them, the risk of catching or transmitting it can be reduced by taking similar precautions to those that prevent the spread of other respiratory pathogens, such as influenza.

This means staying home if you have symptoms, wearing a mask in crowded or poorly ventilated spaces, covering coughs and sneezes with a tissue or bent elbow, and regularly washing hands with soap and water. "People at high risk or with complicated or severe symptoms should seek medical care as soon as possible," WHO said.

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