Human metapneumovirus: how serious is the threat?

China is experiencing a surge in infections of a respiratory virus that is especially dangerous for young children, the elderly and vulnerable groups.

Reports of overcrowded hospitals and people wearing masks have prompted comparisons with the outbreak of Covid five years ago, but human metapneumovirus is far from a mystery illness.

What are the symptoms and how is it spread?

Human metapneumovirus, or HMPV, is a respiratory virus with flu-like symptoms that include a cough, fever and fatigue. With an incubation period of between three and six days, it is one of several viruses often lumped together under a broad definition of the "common cold", Dr Jacqueline Stephens, a senior lecturer in public health at Flinders University in Australia, told The Guardian.

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A single-stranded RNA virus first identified in the Netherlands in 2001, HMPV is spread through respiratory droplets or contact with contaminated surfaces. It is not, however, a "notifiable disease like Covid-19 or influenza".

The illness is "typically mild", said The Independent, but it can lead to "severe complications such as pneumonia, particularly in infants, the elderly, and those with weakened immune systems".

There is currently no vaccine and treatment is focused on alleviating symptoms.

How dangerous is the new outbreak?

According to a 2021 study, 3%-10% of hospital admissions globally in 2018 and 1% of acute lower respiratory infection-related deaths in children aged under five were attributed to HMPV. The study also found that children under six months, especially those in low- and lower-middle-income countries, are at greater risk of death caused by the HMPV virus.

Beijing has downplayed the virus as an annual winter event. "Respiratory infections tend to peak during the winter season," China's foreign ministry spokesperson Mao Ning said on Friday. The apparent increase in cases is "likely partly due to new technology more easily detecting and identifying HMPV", according to experts who spoke to The Guardian.

The spike in cases "coincides with colder weather and increased indoor activity, conditions that typically fuel the spread of respiratory viruses", said The Independent. But China was "widely criticised for covering up details about the early stages of the Covid outbreak in the central city of Wuhan", said The Times.

Should we be worried in the West?

Unlike Covid-19, which was a completely new disease, HMPV has "been around for several decades and there is a level of immunity in the global population from past infections", said The Guardian.

Nevertheless, neighbouring countries including Cambodia and Taiwan are keeping a close watch on the situation. Indian media is "awash with reports" of an "outbreak" in China, said The Hindu, but health officials have said there is no need for panic as HMPV is "like any other respiratory virus".

In the UK, official data from the Health Security Agency revealed that 4.5% of swabs sent to sentinel labs in the last week of December tested positive for HMPV, with the highest positivity in those aged under five. The trend for HMPV is "increasing slightly", said the agency.