Rising concerns over Human Metapneumovirus (HMPV): a Global overview

In recent weeks, questions have arisen about the potential danger posed by HMPV infections. A reported increase in cases in northern China has sparked immediate concern over another Covid-style pandemic. Nonetheless, there is no reason to panic, as various authorities are closely monitoring the situation. The World Health Organization (WHO) has confirmed ongoing contact with Chinese health authorities and has received no reports of unusual outbreak patterns.

This backdrop underscores the need to understand HMPV more comprehensively. Below, we explore the virus’s characteristics, symptoms, and current advancements in vaccine development.

What is HMPV?

HMPV is a single-stranded RNA virus of the Pneumoviridae family. It was discovered in 2001 when it was isolated from a pediatric patient with resembling human respiratory syncytial virus (HRSV). Since then, HMPV has been detected in 4 to 16% of patients with acute respiratory tract infection (ARIs).

While HMPV primarily affects children, it can also infect adults, especially immunocompromised individuals. Clinical features vary from mild upper respiratory illness to serious lower respiratory illness, such as bronchiolitis and pneumonia. According to estimates, HMPV is responsible for 10% to 12% of respiratory illnesses in children, with 5% to 16% of cases leading to lower respiratory tract infection.

Recognizing the symptoms

The severity of HMPV infection often depends on the patient’s age and immune status. For young children encountering the virus for the first time, the risk of serious illness is higher. However, subsequent infections are usually milder.

Common symptoms include:

• Fever
• Cough
• Sore throat
• Dyspnea
• Rash

Adults with pre-existing respiratory conditions, weakened immune systems, or advanced age are also at risk of developing severe symptoms.

Current treatment and Vaccine perspectives

Currently there aren’t approved antiviral treatments or vaccines for HMPV. However, significant progress has been made in vaccine development, particularly in preclinical animal studies. Here are the main approaches being explored:

1. Live attenuated vaccines Researchers have genetically modified HMPV strains to attenuate their virulence while preserving immunogenicity. These modified strains have demonstrated protection in various animal models.
2. Subunit vaccines and virus-like particles (VLPs) vaccines
   • Subunit vaccines using the soluble HMPV fusion (F) protein have shown promise, eliciting neutralizing antibody responses and offering protection in cotton rats and Syrian golden hamsters
   • VLP vaccines incorporating the F protein, either alone or combined with the viral glycoprotein G, have successfully induced protective antibodies in mice
3. Viral-vectored vaccines Using viral vectors such as bovine/human PIV3, human PIV1, and Sendai virus to deliver HMPV F protein, researchers have achieved promising results in animal studies.
4. Epitope-based vaccines A multi-epitope peptide (MEP) vaccine has been designed based on B cell, cytotoxic T lymphocyte (CTL), and T helper (Th) cell epitopes prediction and linked with defined spacer sequences Immunization of mice with this vaccine demonstrated strong humoral and cellular immune responses, effectively neutralizing HMPV in vitro.
5. mRNA vaccines The bivalent mRNA-1653 vaccine, targeting HMPV and PIV3, encodes membrane-anchored fusion proteins of both viruses. Formulated in lipid nanoparticles, it has shown encouraging safety and immunogenicity profiles in seropositive children.