What is hMPV and how widespread is it in the UK?

We’ve seen increased interest in recent weeks in the number of cases of respiratory illness caused by the human metapneumovirus, also known as hMPV.

Some headlines have referred to a “mystery virus”, while some social media posts have claimed that cases are rapidly rising, and asked if there could be a new global pandemic.

In fact, hMPV is a common virus that has been monitored for years, and there are currently no signs of it causing a pandemic. This explainer looks at what hMPV is, what kinds of illness it can cause, and who is most likely to be affected.

What is hMPV?

Human metapneumovirus, or hMPV, is a respiratory virus that belongs to the same family of viruses as RSV (respiratory syncytial virus). It is believed to be seasonal with most infections occurring in the winter months. Most children have been found to be infected with hMPV by the age of five years, but reinfection can occur in older children and also in adults.

Although it was initially identified in the early 2000s, subsequent research has shown that hMPV has been infecting humans for at least 50 years.

How harmful is it to humans?

hMPV can spread through close contact via sneezing, coughing and touching infected surfaces. Symptoms vary from mild cold-like features such as a runny nose, sore throat and cough to more serious illness such as pneumonia and bronchitis. It can take three to six days from exposure for symptoms to appear.

Most cases of hMPV cause mild illnesses, with recovery beginning within a few days. Less commonly, some people may need to be hospitalised and require treatment with additional oxygen. Complications, including life threatening illness, are rare, but more common in children, the elderly and people who are immunocompromised.

Although there is currently no vaccine against hMPV or any specific antiviral therapy, vaccine trials are underway in the UK for a combined hMPV and RSV vaccine.

How widespread is hMPV currently?

The WHO monitors trends in respiratory infections and reported in early January that the increase in infections with hMPV was within the expected range for this time of year. Additionally, after some reports of a surge of cases in China, it made contact with Chinese health authorities who said they were not experiencing unusual outbreaks or indeed any overburdening of their health service.

There is usually an increase in respiratory infections during the winter months, including a rise in hMPV infections.

Commenting via the Science Media Centre, Dr Andrew Catchpole, Chief Scientific Officer at research organisation hVIVO said earlier in January: “Whilst hMPV does mutate and change over time with new strains emerging, it is not a virus that we consider to have pandemic potential…

“Young people have less developed immune systems and the elderly’s immune systems’ effectiveness has declined from when they were younger, hence they become more susceptible to more serious outcomes of infectious diseases.”

The UK Health Security Agency also monitors trends for common respiratory viruses. It reported that the weekly positivity rate for hMPV tests had risen to about 4.9% in mid January.

Although this is the highest rate recorded in the past year, positivity rates have been higher in the past. The UKHSA said on 28 January: “Our regular monitoring systems show that the virus is following its usual seasonal pattern in the UK.”

The European Centre for Disease Prevention and Control has said that there are no specific concerns for Europe and that the situation in China represents a seasonal rise in infections caused by common pathogens.