What is hMPV, the virus spreading through China?

Alarmist headlines that warn of China once again being overwhelmed by a mysterious new virus have dominated in the past few days. But the virus reported to be responsible for a surge in respiratory infections there, called human metapneumovirus, or hMPV, is actually neither mysterious nor new, and authorities in China have rejected claims that its health system is overwhelmed.

What is human metapneumovirus?

It is one of the many different viruses known as cold viruses because they infect the cells lining our respiratory tract, causing “common cold” symptoms, such as a sore throat, runny nose, coughing and sneezing, which may persist for a few days. You have almost certainly had an hMPV infection – studies of antibodies show that just about everybody gets infected by it by the age of 5. As with flu, people can be reinfected throughout their lives as immunity fades and new variants evolve.

How dangerous is hMPV?

In most people it only causes mild symptoms, but, like other cold viruses, it can occasionally be more serious and even deadly. Severe infections usually occur in people who are vulnerable for some reason, including very young children, older people and those with an impaired immune system or conditions such as asthma.

Globally, the virus is estimated to have killed at least 11,000 children aged under 5 in 2018. For comparison, another cold virus called respiratory syncytial virus, or RSV, is estimated to kill 60,000 children globally every year.

How long has hMPV circulated in people?

It has probably been spreading in humans for centuries. The virus was first discovered in 2001, in samples taken from children in the Netherlands who had respiratory infections. Since then, it has been found in stored samples from as early as 1976, while antibodies to the virus have been found in blood samples from the 1950s.

Where did it come from?

Closely related viruses known as avian metapneumoviruses circulate in birds and the human metapneumovirus is thought to have evolved from one of these. However, this is thought to have occurred around 200 years ago, so the situation with hMPV is very different to that with the covid-19 virus, which only jumped to humans in late 2019. While hMPV is now a human virus, it can infect some other animals, including chimpanzees and gorillas.

What kind of virus is it?

It belongs to a group called paramyxoviruses, which consist of a single strand of genetic material in the form of RNA enclosed in a protein coat. Other paramyxoviruses include measles and Nipah. The genome of hMPV is around 13,000 “letters” long and codes for just nine proteins – meaning it has a relatively small, streamlined genome, like many other respiratory viruses.

Is there a treatment or vaccine against hMPV?

There are no specific treatments for hMPV infections or any approved vaccines. However, several potential vaccines are being developed. For instance, in 2024 a team at the University of Oxford began testing an mRNA vaccine designed to protect children against both hMPV and RSV.

Why are there so many cases in China?

It is normal for waves of cold and flu infections to occur during winter, and some years these waves are larger than others for reasons that aren’t well understood. More infections overall mean there will be more severe cases and therefore more hospital admissions. “There’s nothing to indicate anything abnormal. So far, it looks like the normal endemic seasonal nasties doing what they do,” writes Ian Mackay at the University of Queensland in Australia, who points out that there was a similar scare in 2023.

How do we know we aren’t seeing the start of another pandemic?

The covid-19 virus was a new virus, meaning people had no immunity to it. This allowed it to spread widely and made it more likely to cause severe infections. By contrast, the hMPV variant spreading in China reportedly only varies from other hMPVs by a few mutations, meaning most people – apart from young children – already have some immunity.

There have been claims that this new variant is more likely to cause severe infections, but even if true, this doesn’t mean it will cause another pandemic. In fact, Mao Ning, a spokesperson for China’s foreign ministry, said on 3 January that the respiratory infections “appear to be less severe and spread on a smaller scale compared with the previous year”.