After COVID-19, should we worry about metapneumovirus ?

© Polina Tankilevich/Pexels

You have certainly noticed that a new wave of respiratory infections is taking place in northern China, due to human metapneumovirus (HMPV) infections. A health situation that inevitably brings us back to the COVID-19 period, a pandemic that we are not likely to forget any time soon. However, the two health situations are quite distinct, and the World Health Organization (WHO) is rather reassuring about the current facts.

Even though it is part of the list of pathogens designated as priority (available here), it has classified it as low to medium risk. For the moment, it does not therefore constitute a real threat likely to cause a public health emergency of international concern (PHEIC), i.e. a global health crisis.

Molecular structure and transmission dynamics of HMPV

The human metapneumovirus, identified in 2001, belongs to the family of Pneumoviridae, a group of respiratory viruses whose genomic structure deserves particular attention. Its genome, consisting of single-stranded RNA of negative polarity, requires transcription into messenger RNA before any protein synthesis – a mechanism that directly influences its capacity for replication in host cells.

In order for the infected cell to “read” and use this blueprint to make new viruses, it must first be “flipped” so that it is the right way up. It's a bit like trying to build something with instructions written upside down: you first have to copy them the right way up before you can start. This process therefore slows down its replication slightly.

The transmission mechanisms, mainly by respiratory aerosols, involve viral particles between 5 and 10 micrometers in size. These droplets, carrying the viral material, can remain suspended in the air for several hours, particularly in closed and poorly ventilated environments. HMPV is transmitted mainly through the air, when we cough or sneeze.

Schematic showing the surface proteins (G, F) responsible for infection and ;#8217;genome organization encoding key proteins for replication. © Nagarjuna R. Cheemarla and Antonieta Guerrero-Plata/Wikipedia

HMPV: an enemy of the respiratory tract

HMPV is a virus that particularly affects the cells that line our respiratory tracts, such as the nose and lungs. To understand how it works, imagine the virus as a key looking for its lock: it has special proteins on its surface (glycoproteins F and G) that allow it to attach to respiratory cells and #8217;enter it. This is why the symptoms mainly manifest themselves in the nose, throat, and lungs.

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Just like COVID-19, some people are more susceptible to this virus than others. Young children under two years of age are particularly vulnerable because their immune system is still under construction – like an army that does not yet have all its soldiers (lymphocytes) well trained.

Similarly, people whose immune system is weakened, whether due to cancer treatment, a transplant or HIV, are at greater risk of developing severe forms of the disease because their protective system is less effective. « The youngest and the oldest are at greatest risk, as are people who are immunocompromised, meaning those with weakened immune systems ” explains Dr Harris in this WHO publication about HMPV.

Lessons from COVID-19 to limit the spread of HMPV

The COVID-19 era has provided us with essential experience to better manage HMPV, particularly in three key areas. First, virological surveillance systems, which were significantly strengthened during the pandemic, now allow for earlier detection of respiratory pathogens. Real-time analysis of viral sequences, initially developed for SARS-CoV-2, is now being applied to HMPV, facilitating the monitoring of mutations and the assessment of epidemic risks.

Second, the understanding of airborne transmission mechanisms, deepened during the COVID-19 crisis, directly influences HMPV prevention strategies. Ventilation protocols, mask wearing and physical distancing, scientifically validated against SARS-CoV-2, show comparable efficacy against HMPV.

Finally, the global research infrastructure, mobilized during the pandemic (with more than 240 daily publications on COVID-19), maintains today a strong vigilance on emerging respiratory viruses. This continuity of research, essential in the face of the thousand weekly deaths still attributed to COVID-19, will directly benefit the understanding and management of HMPV.

For the moment, there is therefore no need to panic. ” The levels of respiratory infections reported in China are within the usual range for the winter season ” explains the WHO. According to data provided by Beijing to the institution, the pressure on hospitals is less than last year at the same time. No emergency measures have therefore been put in place. The virus that worries Chinese authorities the most is a much better-known one: influenza, which is on the rise.

• A wave of human metapneumovirus (HMPV) infections in China remains under control, but does not pose an immediate global threat.
• HMPV mainly targets the respiratory tract and affects vulnerable populations such as children and the immunocompromised.
• The lessons learned from COVID-19, particularly on surveillance and prevention, will help to better manage the spread of this virus.

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