A surge in cases of the flu-like human metapneumovirus (HMPV) in China has raised fears of another Covid-style pandemic.

Images of hospitals overrun with masked patients have circulated widely on social media, but health experts say HMPV is not like Covid, and point out it has been around for many years.

They say China and other countries are simply experiencing the seasonal increase in HMPV typically seen in winter.

First identified in the Netherlands in 2001, HMPV spreads through direct contact between people, or when someone touches a contaminated surface.

The virus leads to a mild upper respiratory tract infection for most people.

It is usually almost indistinguishable from flu.

Symptoms for most people include a cough, a fever and blocked nose.

The very young, including children under two, are most vulnerable to the virus.

It also poses a greater risk to those with weakened immune systems, including the elderly and those with advanced cancer, according to Hsu Li Yang, an infectious diseases specialist in Singapore.

If infected, a “small but significant proportion” of immunocompromised people can develop more severe disease where the lungs are affected, with wheezing, breathlessness and symptoms of croup.

“Many will require hospital care, with a smaller proportion at risk of dying from the infection,” Dr Hsu said.

Like many respiratory infections, HMPV is most active during late winter and spring.

This is because viruses survive better in the cold, and can pass more easily from one person to another as people spend more time indoors with closed windows.

In northern China, the current HMPV spike coincides with low temperatures that are expected to last until March.

Many other countries in the northern hemisphere – including the US – are also experiencing a growth in rates of HMPV, said Jacqueline Stephens, an epidemiologist at Flinders University in Australia.

“While this is concerning, the increased prevalence is likely the normal seasonal increase seen in winter,” she said.

The World Health Organization (WHO) is monitoring rates of flu-like illness across the Northern hemisphere, and said it has not received any reports of unusual outbreak patterns in China or elsewhere.

It said Chinese authorities have confirmed that the health care system is not overwhelmed and there have been no emergency declarations or responses to date.

The incidence of HMPV in the UK has risen steadily since October 2024.

The UK Health and Security Agency (UKHSA) does not publish the number of cases recorded.

However its latest data shows the percentage of people testing positive for the disease rose sharply in the third week of December and remained at that higher level the following week.

But the UKHSA says this is completely in line with normal seasonal trends, and the level of the disease being seen in GP surgeries and hospitals is as expected.

Fears of a Covid-style pandemic are overblown, experts say, noting that such events are typically caused by new viruses, which is not the case with HMPV.

The disease is already globally present and has been around for decades. This means people across the world have “some degree of existing immunity due to previous exposure”, Dr Hsu said.

“Almost every child will have at least one infection with HMPV by their fifth birthday and we can expect to go onto to have multiple reinfections throughout life,” said Paul Hunter, a medical professor at University of East Anglia in England.

“I don’t think there are currently any signs of a more serious global issue.”

However, health officials recommend taking sensible precautions to avoid catching HMPV and other respiratory illnesses:

• wearing a mask in crowded places
• avoiding crowds where possible if you are at higher risk of more severe illness
• washing your hands regularly
• disposing of tissues securely

People may also wish to consider getting vaccinated against other respiratory conditions such as the flu.

In the UK, pregnant women and adults aged 75 to 79 are advised to get the respiratory syncytial virus (RSV) vaccine.

RSV is a common infection that causes coughs and colds, but can sometimes be serious for babies and older adults.