hMPV Cases Rise Across China, But Experts Warn Against Panic
Increases in hMPV cases across Asia have sparked concerns over a potential pandemic, which experts argue are unfounded.
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Headlines have been flooded with warnings of a surge in human metapneumovirus (hMPV) cases in China, but experts say the situation shouldn’t trigger fears of a larger pandemic threat.
hMPV is a respiratory virus that causes flu or cold-like symptoms. It is most common during the winter months when the seasonal increase of flu-like respiratory illnesses occurs.
The Chinese Centre for Disease Control and Prevention (CDC) recently reported a sharp increase in respiratory viral infections, including hMPV, in Northern China since December 2024. This coupled with reports of hospitals in China allegedly flooded with cases has further fueled attention to this lesser known, yet common, winter disease.
But hMPV is not like COVID-19, experts have said, noting that the increased prevalence is likely the normal seasonal increase seen in winter.
While symptoms are often mild, the virus can cause more serious illness in individuals with weakened immune systems, the very young or the elderly, which have prompted calls for enhanced surveillance and prevention strategies.
What is hMPV?
hMPV was first discovered in the Netherlands in 2001 when researchers found evidence that most children are exposed to the virus by age five. It belongs to a group of viruses called paramyxoviruses, which are single-stranded RNA viruses.
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The virus is closely related to avian metapneumovirus (aMVP) and genetic analysis has indicated that hMPV likely originated from aMVP 200 to 400 years ago. The virus has since evolved to adapt to its human host, to the degree that the human form can no longer affect birds.
hMPV is spread like other flu-like illnesses – by airborne droplets produced when an infected person breathes, coughs or sneezes.
What are the symptoms of hMPV?
Clinical symptoms of the virus are usually mild and like those caused by human respiratory syncytial virus (RSV) infection. While most cases lead to flu-like symptoms, it can sometimes cause lower respiratory infections like pneumonia, asthma flare-ups or worsen chronic obstructive pulmonary disease. Like the flu, people can be reinfected as immunity fades and new variants evolve.
“As a respiratory virus, hMPV triggers both innate and adaptive immune responses,” said Dr. Vasso Apostolopoulos, a professor of immunology at RMIT University. “The innate response activates interferons and cytokines to control viral replication, while the adaptive response produces virus-specific antibodies and T cells. However, individuals with weakened immune systems, the very young or the elderly may have slower or less effective immune responses, increasing the risk of severe complications such as pneumonia, bronchiolitis or exacerbations of other respiratory conditions.”
Are we witnessing the start of the next pandemic?
As with many respiratory viruses, hMPV is most active during winter. “Contributing factors to the outbreak [in China] may be due to increased vulnerability to co-infections (such as RSV and influenza) and seasonal/environmental conditions like cold weather, which facilitate viral transmission,” explained Apostolopoulos.
The current spike in hMPV cases in Northern China coincides with low temperatures that are expected to last until March. Experts believe the increased prevalence is likely the normal seasonal increase seen in winter for many flu viruses.
Unlike SARS-CoV-2 – the virus responsible for the COVID-19 pandemic – hMPV has been present in the human population for decades. This means that most people – apart from young children – already have some immunity against the virus.
“This is very different to the COVID-19 pandemic, where the virus was completely new in humans and arose from a spill-over from animals and spread to pandemic levels because there was no prior exposures or protective immunity in the community,” said Professor Jill Carr, a virologist at Flinders University.
While hMPV may not be a risk to most people, some people can have poor outcomes. In addition, there are currently no specific treatments for hMPV infections or any approved vaccines. However, several vaccines are in development including an mRNA vaccine designed to protect children from both hMPV and RSV.
In addition, growing case numbers can put pressure on healthcare systems in densely populated regions. For these reasons, experts caution that effective monitoring and timely responses are still essential and will be key to mitigating the public health risks of the outbreak.
Carr believes it is vital that China share its data on the outbreak in a timely manner; “This includes epidemiologic data about who is getting infected. Also, we will need genomic data confirming that hMPV is the culprit and that there aren't any significant mutations of concern. Such genomic data will also guide vaccine development."
Overall, signs don’t point to a more serious global health issue but learnings from the pandemic such as “good hand hygiene, good sneeze and cough etiquette and wearing a face mask in public places,” said Dr. Jacqueline Stephens, associate professor at Flinders University, will be important to try to reduce transmission in affected regions.
