But HMPV typically circulates in the Northern Hemisphere in winter, and China’s CDC data shows that there have also been rises in a number of other common respiratory infections, including the seasonal flu and respiratory syncytial virus, or RSV.

“China’s reported levels of respiratory infections are within the normal range. It’s what we would expect to see for the winter season,” Margaret Harris, a spokesperson for the World Health Organisation, said in a news briefing on Tuesday.

To calm concerns, she added that hospital utilisation in China is lower than at this time last year and that there have been no emergency declarations or emergency responses launched in the country in connection with these respiratory infections.

“Regarding human metapneumovirus, it’s not a new virus,” Harris said.

“It was first identified in 2001. It’s been in the human population for a long time. It is a common virus that circulates in winter and spring.”

In the United States, the CDC tracks cases of HMPV in the same way it tracks the spread of other respiratory viruses.

It’s estimated that about 10 per cent to 12 per cent of respiratory illnesses in children are caused by HMPV; most people will get HMPV at some point before age 5, and then reinfections can occur throughout life.

Data shows that HMPV cases started to show up more frequently in November and have been rising since.

But, compared with other common viruses, the weekly percent of respiratory infections testing positive for HMPV has been low, at 1.94 per cent as of December 28. In comparison, flu was at 18.71 per cent and Covid-19 at 7.10 per cent that week.

“It’s respiratory virus season for a reason. We’ve gotten very accustomed to thinking about those that have been really severe – so Covid, as well as flu and RSV – but there are a host of other respiratory viruses out there that you can get sick with,” said Janet Hamilton, executive director of the Council of State and Territorial Epidemiologists.

When it comes to common respiratory infections like HMPV, “many times, you get better on your own, but not necessarily always,” Hamilton said.

“Typically, infections are relatively mild, and we often think about it like the common cold,” she added.

“Many people don’t necessarily know when they have a common cold that it is caused by human metapneumovirus, but it’s definitely one of the viruses that are often associated with the common cold.”

Some of the symptoms commonly associated with HMPV infections include cough, fever, stuffy nose and shortness of breath.

How does the virus spread?

HMPV spreads from person to person in a similar way as some other respiratory viruses: through droplets from coughing or sneezing and through touch, such as shaking hands or touching contaminated surfaces.

“Simple measures can prevent spread. And these include, if you’re sick, if you’ve got symptoms, stay home,” Harris said.

“Also, if you’re in crowded or poorly ventilated spaces, when you know that there’s a virus currently circulating, think about wearing a mask. Improve ventilation where you can,” she said.

“And of course, cover coughs and sneezes with a tissue.”

Some people are at increased risk of severe infections with HMPV, Harris said.

“In some cases, like any of the common cold viruses, it can lead to more severe disease in people who’ve got no immunity or have got very weak immune systems,” she said.

“That’s the very young. That’s newborn babies – that’s why you don’t go and visit a newborn baby and kiss it when you’ve got a cold – and the very old. Again, that’s why you should not go and visit your over-90 great-grandmother in hospital when you’ve got a cold.”

How is HMPV treated? Is there a vaccine?

Health care providers can test for HMPV, but there is no vaccine, and there is no specific antiviral therapy to treat infections. Resting at home and staying hydrated can help with symptoms, as well as some over-the-counter medications.

Mild cases of HMPV usually last a few days to a week, and many people recover by themselves within two to five days.

“If you do feel very unwell go to your GP,” he said.

“As it is a virus, antibiotics won’t have any effect.”