Is There Cause for Concern?

The Chinese Centre for Disease Control and Prevention has reported a sharp rise in respiratory viral infections since December 2024, including from human metapneumovirus (hMPV), drawing widespread media attention and flashbacks to January 2020.

However, most experts agree that the likelihood of a COVID-like pandemic is low because variants of hMPV have circulated for decades, and many people have at least some level of immunity.

“Seasonality is similar to that of influenza, with peak activity in winter and early spring. Therefore, the high number of hMPV cases identified in China may not be out of the ordinary,” said Antonia Ho, MBChB, PhD, a professor and honorary consultant of infectious diseases at the Medical Research Council-University of Glasgow Centre for Virus Research, speaking to the UK’s Science Media Centre (SMC).

“Our surveillance systems in GP surgeries and hospitals indicate that levels are in line with what we would expect to see. Most people have had hMPV by the time they are 5 years old and catch it again throughout their lives,” added Conall Watson, PhD, consultant epidemiologist at the UK Health Security Agency, also speaking to the SMC.

Why Is hMPV in the News?

hMPV is a negative-sense single-stranded RNA virus belonging to the family Pneumoviridae. It was first identified in 2001 in the Netherlands and is closely related to avian metapneumovirus subgroup C. It spreads primarily through direct contact with respiratory secretions from infected people or by touching contaminated surfaces. It can lead to mild upper respiratory infections with flu-like symptoms, including cough, fever, nasal congestion, and sore throat. 

Most infections are mild, typically lasting 2-5 days. However, severe cases can occur, especially in infants younger than 12 months; older adults; and people with immunodeficiencies and comorbidities, such as hypertension, diabetes, obesity, cardiovascular disease, and chronic respiratory disease. Severe symptoms may include wheezing, shortness of breath, bronchiolitis, and pneumonia.

The rise in hMPV infections in China has received widespread media coverage. Photos and videos posted on social media showing overcrowded hospitals have led to concerns about another pandemic looming. But hMPV typically circulates in the Northern Hemisphere in winter, and data from China show that cases of other common respiratory infections, including the seasonal flu and respiratory syncytial virus, have also increased.

As with other respiratory viruses, the COVID-19 pandemic restrictions resulted in the cessation of hMPV circulation for almost 2 years, creating a so-called “immune debt” — that is, the waning of general population immunity and the formation of groups of hMPV-naive children, Alessandra Pierangeli, PhD, a research scientist and associate professor of microbiology and virology at Sapienza University of Rome, told Medscape Medical News. “The immune debt was probably responsible for the resurgence of hMPV infection and the changes in seasonality observed after the restrictions were completely lifted in 2022,” she said. 

In the last epidemic season (2023-2024), the circulation of respiratory viruses, including hMPV, returned to the usual pre-COVID patterns, but Pierangeli said more data are needed to understand hMPV epidemiology and genetic evolution. “The extent of the hMPV disease burden remains poorly defined due to a lack of national and global data. As a result, it is difficult to compare data from the current outbreak in China with those from the past.”

The prevalence of different subtypes of hMPV can vary significantly from one epidemic season to another. Like many respiratory viruses, hMPV can undergo mutations and recombination, leading to the emergence of new strains. Recently, variants with 111- and 180-nucleotide duplications in the G gene have become increasingly prominent worldwide. These genetic changes produce additional amino acids in the virus’s outer envelope. 

Although these new variants are antigenically distinct from earlier strains, they do not cause more severe illness. However, Pierangeli said they can reinfect people despite their immunity from previous infections. 

“The hMPV is an RNA virus like many other respiratory viruses and, as such, it can mutate. However, this does not imply that it can necessarily cause public health emergencies,” Piotr Kramarz, PhD, chief scientist at the European Centre for Disease Prevention and Control (ECDC), told Medscape Medical News.

What Risks Does hMPV Pose to Europe?

From September 2022 to August 2024, the Italian Working Group on Respiratory Viral Infections (GLIViRe) found a cumulative hMPV positivity rate of 3.4%. The hMPV epidemic peaked in late winter/early spring and, during the peak, the overall hMPV positivity rate was around 12% of acute respiratory infection cases. Although hMPV circulation is still low in Italy, Pierangeli said a similar pattern is expected this year. 

The ECDC reassures that the current epidemiologic situation in China reflects a seasonal rise in respiratory infections caused by common respiratory pathogens and does not pose any specific concern for Europe. 

“hMPV is a common and known respiratory virus that regularly circulates in Europe during colder months. Illness caused by human metapneumovirus is not a notifiable disease in the EU,” Kramarz said. “The surveillance of acute respiratory infections shows the expected increased activity of respiratory viruses, particularly influenza, during this time of year with no unusual or unexpected pattern.”

On December 18, 2024, the ECDC released an update regarding acute respiratory infections within the EU, advising member states to prepare for a rise in respiratory virus cases in the upcoming winter weeks and to implement infection prevention and control measures aimed at reducing transmission in healthcare environments, including long-term care facilities.

Ho, Pierangeli, Kramarz, have disclosedno relevant financial relationships. Watson did not respond to the SMC’s request for a declaration of interests.

Manuela Callari is a freelance science journalist specializing in human and planetary health. Her words have been published in The Medical Republic, Rare Disease Advisor, The Guardian, MIT Technology Review, and others.