What is hMPV, the virus spreading through China?

Alarmist headlines that warn of China being once again being overwhelmed by a mysterious new virus have dominated over the past few days. But the virus that is reported to be responsible for a surge in respiratory infections in China, 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, or hMPV?

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 sold 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 hMPV by the age of five. 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 will cause only mild symptoms, but like other cold viruses, it can occasionally be more serious and even deadly. Serious 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 five 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 this virus circulated among people?

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

Where did the virus 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 bird viruses. 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 hMPV?

It belongs to a group of viruses called paramyxoviruses, which consist of a single strand 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, nor 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 are not 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 are not 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 hMPV variant is more likely to cause severe infections, but even if true, this does not mean it will cause another pandemic. In fact, Mao Ning, a spokesperson for the Chinese 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”.