A neglected respiratory virus sends adults to hospital about as sick as RSV

Respiratory syncytial virus has become a familiar name in adult medicine, with new vaccines and antibody products built around it. Human metapneumovirus, a close relative that causes similar illness, has stayed in the background — rarely tested for, rarely discussed. A retrospective analysis of Scottish national hospital data argues that this neglect is hard to justify: once a patient is sick enough to be admitted, the two viruses look broadly alike [s1].

Human metapneumovirus (hMPV) was identified only in 2001 and circulates each winter alongside RSV and influenza. There is no licensed hMPV vaccine, and because many hospitals do not routinely test for it, its contribution to winter respiratory admissions has been easy to overlook. The Scottish study set out to measure that contribution directly, before RSV vaccines were introduced [s1].

What the study did

Researchers conducted a retrospective cohort study of adults aged 18 and over using routinely collected, linked national laboratory, hospital, intensive-care and mortality data in Scotland, covering 1 July 2017 to 30 June 2023 [s1]. Comorbidity status was defined using UK influenza clinical risk groups, and negative binomial regression was used to estimate adjusted hospitalisation rates by virus, age, comorbidity burden and season [s1]. Separate logistic-regression models examined whether the infecting virus was associated with a long hospital stay, admission to intensive care or a high-dependency unit, and death within 90 days [s1].

The findings

RSV was detected far more often than hMPV among hospitalised adults: the relative rate ratio for laboratory-detected hospitalisation was 2.31 (95% confidence interval, 2.20 to 2.43) in favour of RSV [s1]. On its face that makes RSV the bigger problem. But the authors are explicit that this difference "likely reflect[s] testing variation" — RSV is tested for more routinely than hMPV, so part of the gap is an artefact of what clinicians look for rather than a true difference in how often each virus puts people in hospital [s1].

Hospitalisation rates for both viruses rose with advancing age, particularly among adults aged 65 and over, and climbed with each additional underlying condition; they also varied substantially by season, with marked reductions during the COVID-19 pandemic and a resurgence in 2022/23 [s1].

When the analysis turned from how often each virus was found to how sick those patients were, the gap closed. Compared with hMPV, RSV was associated with lower odds of a prolonged hospital stay and of intensive-care or high-dependency admission, and there was no substantial difference in 90-day mortality between the two [s1]. In plain terms, patients admitted with hMPV were at least as likely to have a severe course as those admitted with RSV. Across both viruses, the strongest predictors of a bad outcome were not which virus a patient had but how old they were and how many underlying conditions they carried [s1].

A companion analysis using the Global Burden of Disease 2021 framework placed hMPV alongside influenza, RSV, SARS-CoV-2 and other viruses as one of five categories driving viral lower respiratory disease worldwide between 2010 and 2021 across 204 countries and territories — a recognition that hMPV belongs in the same conversation as the pathogens that attract vaccine programmes, not a tier below them [s2].

Who funded it

Both the Scottish analysis and the global burden estimate were funded by AstraZeneca, which markets respiratory products including an RSV monoclonal antibody [s1][s2]. That matters to how the results are read. A finding that hMPV is under-recognised and comparably severe is one that could support a commercial case for expanding diagnostics or developing hMPV products, so the funding is worth stating plainly even though the underlying design — linked national records, pre-specified regression models — is the kind that is hard to bend toward a conclusion [s1].

What it means

The useful signal here is not a ranking of two viruses but a correction to a blind spot. If hMPV is tested for less often yet lands comparably sick patients in hospital, then surveillance built around RSV alone understates the winter respiratory burden [s1]. The study's own limits are real: it is observational, confined to hospitalised patients in one country, and its headline incidence gap is shaped by testing practices the authors cannot fully adjust away [s1]. It cannot say how many hMPV infections never reach hospital, and it predates RSV vaccination, so it describes the era just before the tools for one of these viruses changed. What to watch is whether health systems broaden routine respiratory testing to count hMPV properly — the first step before anyone can judge whether it, too, warrants a vaccine. Readers should treat hMPV as a real but still poorly measured contributor to winter illness, not a settled one.

Sources

• [s1] Hospitalisation Burden of Human Metapneumovirus and Respiratory Syncytial Virus in Adults by Age and Comorbidity Status in Scotland: A Retrospective Analysis. Infectious Diseases and Therapy, 2026. https://doi.org/10.1007/s40121-026-01410-8
• [s2] Global Viral Lower Respiratory Disease Episodes, Hospitalisations, and Clinical Outcomes by Aetiology, 2010-2021. Infectious Diseases and Therapy, 2026. https://doi.org/10.1007/s40121-026-01406-4