What to know about the HMPV outbreak in China

Reports of an outbreak of human metapneumovirus (HMPV) in parts of China are drawing international attention.

HMPV was identified by a research group in the Netherlands in 2001, and had likely spread among humans for many years prior to that.

News of the current outbreak followed an announcement by China’s National Administration of Disease Control and Prevention that it was testing a new reporting protocol in response to pneumonia cases.

At a news conference reported by the state broadcaster CCTV, health officials noted that several common infections were circulating within China during the cold months and issued warnings about relying on antiviral medications to address the diseases.

What is the current situation with HMPV?

The current HMPV situation in China is a new outbreak of a known and relatively well-understood virus that has likely circulated among humans for hundreds of years.

HMPV cases have reportedly surged among young people in northern parts of China in recent weeks. Cases of rhinoviruses, a major cause of common colds, have also risen.

Across the border, India’s Health Ministry has confirmed two cases of HMPV in the state of Karnataka, but said in a media release that HMPV is endemic across the world, and that no "unusual surge" of flu or severe respiratory disease cases had been reported in the country.

Epidemiologists elsewhere have also tempered suggestions of a major health emergency.

"The increased prevalence is likely the normal seasonal increase seen in winter. The reported high prevalence amongst children also reflects what we know about this virus: It is a common cause of childhood respiratory illness," said Jacqueline Stephens, an epidemiologist at Flinders University in Australia.

Jill Carr, a virologist also from Flinders University, said the HMPV outbreak in China was very different from the coronavirus pandemic, in which the virus was completely new in humans and there was no protective immunity.

Similar to RSV

HMPV comes from the same viral family as respiratory syncytial virus (RSV), which also causes short-term infections.

Like RSV, HMPV is a seasonal infection occurring in the colder months with the potential to reach epidemic levels, when a high rate of infection occurs at a particular point in time.

Until a Dutch-led research group first identified HMPV in 28 Dutch children in 2001, cases were often misdiagnosed as RSV because of their very similar symptoms.

"What we found is that all the children over about 5 years of age had antibodies against this [HMPV] virus," Albert Osterhaus, who led that first study as a member of the Department of Virology at the Erasmus Medical University in Rotterdam, told DW.

Osterhaus, now a virologist with Germany's University of Veterinary Medicine Hannover, and his colleagues have since determined that HMPV has circulated in humans for hundreds of years.

Unlike the coronavirus and influenza, HMPV also appears to be relatively stable. This means that mutations are less frequent, with reinfection occurring over time as immunity wanes.

"Influenza virus is really the champion in mutation," Osterhaus said. "[HMPV] is relatively stable, and we have looked into both RSV and HMPV viruses from 10-15 years ago and we saw some changes, but not major changes."

Symptoms of HMPV

HMPV causes infections in the upper and lower respiratory tract, with symptoms similar to those of RSV.

Symptoms can include cough, fever and congested nasal passages, which are often caused by other viruses, as well. In mild cases, this can make diagnosis difficult.

Pneumonia or bronchitis can result in more severe cases.

Like other respiratory illnesses, HMPV is contagious. Transmission occurs through exposure to airborne droplets expelled when an infected person coughs or sneezes, as well as contact with contaminated surfaces, including by physical contact with hands or skin.

Though anyone can become infected with HMPV, very young children and the elderly are at most risk for developing serious illness.

Is there a treatment or vaccine for HMPV?

There is currently no treatment or vaccine for HMPV.

Preventive measures include good hygiene, avoiding exposure to infected people (and, for infected people, staying home to prevent the spread), and adopting measures such as wearing masks.

A suitable vaccine is in development. Osterhaus said the vaccine might come from a "revolution" for RSV vaccines.

"We know how to make them these days, and so they are used in elderly people, in pregnant women, and it’s being tried to have them for young infants as well.

"For HMPV, I think, in principle, because the virus is very similar to RSV, I expect the companies that are working on developing an RSV vaccine HMPV will be next," he said.

Osterhaus predicts that a HMPV vaccine will be ready "in the coming years".