What Is hMPV, and Could It Be the Next Pandemic?

Human metapneumovirus HMPV molecular closeup in 3d rendering with hospital setting.

(Adobe Stock 1173397419 by Loki Studio)

Human Metapneumovirus (hMPV) is a common winter virus that causes respiratory tract infections, mainly in the pediatric population. However, its impact can be severe for elderly and immunocompromised individuals as well. While it is not a novel respiratory virus and is quite prevalent in children under the age of 5 (second to respiratory syncytial virus (RSV) in causing bronchiolitis), it has been trending in the news due to an unprecedented surge in hMPV infections that began in China in late 2024. Undoubtedly, public awareness of disease outbreaks and effective diagnostic and treatment measures will be crucial to combat the spread of disease.

Background on hMPV
hMPV is a single-stranded RNA virus and is a relatively new member of the Paramyxoviridae family, discovered in 2001.¹ Since its discovery in the Netherlands, its cases have been reported worldwide. Noteworthy, the health care and economic burden imposed by hMPV in pediatric respiratory illness is only second to RSV (which also belongs to the same Paramyxoviridae family).

Both continue to exhibit similarities. Due to their structural similarity and taxonomic proximity within the same family, hMPV is often compared with RSV, discovered decades earlier in 1956. Both viruses present similar clinical manifestations, often collectively addressed as influenza-like illness (ILI),² ranging from mild to moderate upper respiratory infections to severe lower respiratory tract infections (LRTIs) leading to medical intervention and hospitalization.³ HMPV is only second to RSV in LRTI-associated hospitalizations in pediatrics.⁴
Like most respiratory viruses, hMPV starts circulating at the beginning of winter and continues until the end of spring. It spreads via air droplets and close contact with infected individuals.

hMPV recently made international headlines due to an outbreak in China, overwhelming their hospitalization rates.⁵ According to the CDC’s surveillance report, an uptick in hMPV infections has been seen in the US since November 2024.⁶ Why is hMPV trending in the news as this mysterious bug despite being a common winter virus?

The most probable answer is that after the recent global pandemic, every outbreak is considered serious (with a pandemic potential), especially when it pressurizes the health care system. Thanks to the recent pandemic, there is now greater public awareness of the impact of outbreaks. Strategies such as public health education, prevention and safety measures, and advocacy for policies that will help prevent the spread can effectively reduce misinformation and stress during an outbreak.

Detection of hMPV
Since the past decade, nucleic acid amplification tests (NAATs), especially Real-time PCR (especially the syndromic multiplex RT-PCR) for viral respiratory tract infections (VRTIs), have transformed the laboratory diagnosis landscape. Some of the main reasons PCR-based testing has become the mainstay for respiratory viral detections are as follows:⁷

1. High specificity and sensitivity of multiplex PCR tests enable accurate detection of causal pathogens.

2. Most winter viruses present overlapping clinical presentations in an RTI; employing multiplex real-time PCR techniques can help simultaneously detect multiple pathogens from a single specimen.

3. Rapid PCR tests help deliver results to health care providers quickly (usually within 24 hours), bolstering prompt treatment decisions. Viral culture was formerly considered the gold standard for detecting viral species in clinical specimens. However, assessing and reading viral cultures requires specialized expertise and is time—and resource-intensive, with a turnaround time between 3 and 7 days.
hMPV, as a relatively newly emerged virus of global importance, is often skipped for routine testing by clinicians. CDC emphasizes that health care providers test for hMPV during its circulation period (winter to spring).⁸

While molecular detection is the preferred method for hMPV detection in the current testing landscape, rapid antigen tests (comparatively less sensitive than a PCR test) and viral cultures (can take up to a week for results) are also utilized for hMPV detection.^7,9

hMPV Prevention and Treatment
One can prevent themselves from getting hMPV infections by practicing the safety measures recommended by the CDC.⁸ This includes avoiding contact with infected individuals, maintaining hand hygiene,¹⁰ and practicing infection control guidelines as suggested by the CDC.¹¹ No antivirals or vaccines are available against hMPV, and treatment and disease management depend heavily on clinical symptoms. Infection severity may result in hospitalization or oxygen therapy.

Challenges and Future Prospects
Immunizations are the first line of defense against infectious disease prevention, tremendously reducing the health care burden worldwide. The recent pandemic accelerated the vaccine research, with the first RSV vaccines FDA approval from 2023-2024. The respiratory season of 2024-2025 is the first season of respiratory illness, where vaccines against all the 3 common winter viruses (influenza, COVID-19, and RSV) were available.¹³ A few promising hMPV vaccine candidates, including bivalent vaccines (RSV/hMPV), are currently in clinical trials.^12,13,14,15 The main challenges remain vaccine hesitancy and availability.

References
1. Kahn JS. Epidemiology of human metapneumovirus. Clin Microbiol Rev. 2006 Jul;19(3):546-57
2. Thomas RE. Is influenza-like illness a useful concept and an appropriate test of influenza vaccine effectiveness? Vaccine. 2014 Apr 17;32(19):2143-9
3. Boivin G, Abed Y, Pelletier G, et al. Virological features and clinical manifestations associated with human metapneumovirus: a new paramyxovirus responsible for acute respiratory tract infections in all age groups. J Infect Dis. 2002 Nov 1;186(9):1330-4.
4. Boivin G, De Serres G, Côté S, et al. Human metapneumovirus infections in hospitalized children. Emerg Infect Dis. 2003 Jun;9(6):634-40
5. Murphy F. Fact check: Human metapneumovirus in China BMJ 2025; 388:r68
6. CDC. The National Respiratory and Enteric Virus Surveillance System (NREVSS). Accessed January 30, 2025. https://www.cdc.gov/nrevss/php/dashboard/index.html.
7. Jeong S, Park MJ, Song W, et al. Advances in laboratory assays for detecting human metapneumovirus. Ann Transl Med. 2020 May;8(9):608.
8. About human metapneumovirus. CDC. Accessed January 30, 2025. https://www.cdc.gov/human-metapneumovirus/about/index.html
9. Ebihara T, Endo R, Ma X, et al. Detection of human metapneumovirus antigens in nasopharyngeal secretions by an immunofluorescent-antibody test. J Clin Microbiol. 2005 Mar;43(3):1138-41.
10. CDC. Clinical Safety: Hand Hygiene for Health care Workers. Accessed January 30, 2025. https://www.cdc.gov/clean-hands/hcp/clinical-safety/index.html
11. CDC. Infection Control Guidance: Respiratory Viruses. Accessed January 30, 2025. https://www.cdc.gov/project-firstline/hcp/infection-control/index.html#:~:text=Summary%20of%20recommendations,respiratory%20hygiene%20and%20cough%20etiquette
12. Ma S, Zhu F, Xu Y, et al. Development of a novel multi-epitope mRNA vaccine candidate to combat HMPV virus. Hum Vaccin Immunother. 2023 Dec 15;19(3):2293300.
13. August A, Shaw CA, Lee H, et al. Safety and Immunogenicity of an mRNA-Based Human Metapneumovirus and Parainfluenza Virus Type 3 Combined Vaccine in Healthy Adults. Open Forum Infect Dis. 2022 May 1;9(7):ofac206.
14. University of Oxford. Department of Pediatrics. New trial launches for two-in-one vaccine to prevent RSV and hMPV July 12, 2024. Accessed January 30, 2025. https://www.paediatrics.ox.ac.uk/news/new-trial-launches-for-two-in-one-vaccine-to-prevent-rsv-and-hmpv
15. Vicebio Advances Clinical Study of RSV/hMPV Bivalent Vaccine & Strengthens Board with Appointments of World Class Veterans Vicebio. November 21, 2024. Accessed January 30, 2025. https://www.prnewswire.com/news-releases/vicebio-advances-clinical-study-of-rsvhmpv-bivalent-vaccine--strengthens-board-with-appointments-of-world-class-veterans-302311876.html