Human metapneumovirus: Virulence, clinical and societal impact, and the path toward therapeutics and vaccines

Human metapneumovirus, a negative-sense RNA paramyxovirus initially characterised in 2001, appears to constitute a primary global aetiological agent of acute respiratory tract infection across all age demographics. This review provides a comprehensive overview of current knowledge on HMPV literature, focusing on the molecular mechanisms of receptor engagement and membrane fusion including the roles of heparan sulfate proteoglycans, RGD-binding integrins, and priming proteases such as TMPRSS2, matriptase, and KLK5. This review delineates the epidemiological impact of the virus upon children, older adults, and immunocompromised patients, alongside the associated socioeconomic burden. We also evaluated the current landscape of therapeutics and vaccine development. Although the absence of licensed antiviral therapeutics or prophylactic vaccines persists, advancements in the understanding of the fusion glycoprotein, combined with the progression of bivalent respiratory syncytial virus/human metapneumovirus vaccine candidates into clinical trials, underscore the enhanced translational potential of HMPV vaccine development. However, robust evidence of clinical efficacy and safety remains essential for licensure. Ongoing research into viral immunopathogenesis remains critical to overcoming challenges associated with incomplete immunity and frequent reinfections. Furthermore, the significant clinical overlap with alternative respiratory pathogens may necessitate the development of point-of-care molecular diagnostic modalities to enhance surveillance and patient management. Addressing this diagnostic gap through multiplex RT-PCR integration is urgent, as seasonal data often underestimate HMPV's contribution to paediatric hospitalisations. With an annual incidence of 14.2 million lower respiratory tract infections in children under five, HMPV imposes a significant, often under-reported, long-term impact on public health.