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In the last few days there have been reports of yet another infectious disease rapidly spreading in China. This time the virus is human metapneumovirus, abbreviated to HMPV.
There have been claims in some media outlets that this surge in infections is overwhelming hospitals in China . On the other hand, the current wave of infections is not out of the ordinary for this time of the year, according to the World Health Organization.
So what is the real situation and what is HMPV anyway? HMPV is a respiratory virus in the same family as the more commonly known respiratory syncytial virus (RSV). It is not a new infection and has probably been circulating in humans for centuries.
The virus was first linked to human illness about 25 years ago by Dutch researchers who identified the virus in children who had a similar illness to RSV. This same study showed that the virus was not new as archived samples from the 1950s showed that all children in the study had antibodies to HMPV by their fifth birthday. Other research has suggested that HMPV diverged from avian MPV about 300 years ago.
Like all viruses, HMPV evolves over time. But its rate of evolution is relatively slow compared with some other viruses.
HMPV is one of the commoner respiratory viruses. Even after childhood, we can expect multiple repeat infections throughout life.
The disease is found around the world, with most infections occurring during the winter months. The virus causes an illness that is very difficult to distinguish from many other respiratory infections without testing.
Most infections are a mild cold-like illness, and people recover within about two to five days. However, in young children, the illness can be more severe and similar to the chest infection caused by RSV. HMPV in children generally doesn’t cause as severe an illness as RSV and is less likely to require admission to an intensive care unit.
In older adults (over 65), and those with certain existing health conditions, HMPV can cause more severe disease. This is particularly the case in people who have heart and lung disease, including asthma.
There is no specific treatment for HMPV. Instead, patients are made comfortable until they recover on their own. If people become very ill then treatment consists of supporting normal breathing.
There is no vaccine against HMPV. However, several vaccines are in the process of being developed. A combined HMPV and RSV mRNA vaccine has recently started trials.
What is the current situation?
In the UK, HMPV-positive samples increased substantially in the weeks before Christmas rising to 4.5% of samples tested in the last week. The most recent data from the first week of January suggests that infection numbers may have already peaked and the proportion of samples positive remains about 4.5%.
In the same week, 21.9% tested positive for flu, a fall from 27.7% the week previously. The HMPV results for the same week last year and the year before that are about the same. So in the UK at least, levels of HMPV infections seem to be about what we would expect for this time of the year.
We will have to wait to see whether HMPV infections start to decline through January. The situation in the UK is reflected in the US, though as yet rates in the US are still well below last winter’s peak.
In China, reports of HMPV infections have indeed been rising in recent weeks in the more northerly regions. But so have reports of all the other respiratory pathogens including seasonal flu, rhinovirus and RSV.
In China, influenza remains the most commonly detected respiratory virus, just like in the west. In its latest report, the World Health Organization has suggested that, currently, the increase in respiratory pathogens in China is “within the range expected for this time of year”. If health services are being overwhelmed in China, flu is much more likely to be the main concern.
So, I think we can be pretty confident that we are not going to see a substantial additional global risk to public health from HMPV.
The situation with HMPV is very different from the situation with COVID in early 2020. Unlike COVID, HMPV is not a new infection and there is already substantial immunity in most people from many previous infections.
Also, the “F protein” – one of the main targets on the surface of HMPV our antibodies latch on to in order to neutralise it – has remained stable for decades suggesting that a new variant is unlikely.
But we should never be complacent about any infectious disease and so we need to continue to monitor what is happening in China and change our risk assessments if necessary.
Paul Hunter consults for the World Health Organization. He receives funding from National Institute for Health Research and has received funding from the World Health Organization and the European Regional Development Fund.
