Publication date: Jul 16, 2025

Understanding temporal trends of influenza and human metapneumovirus (HMPV) infections among adults and their return after the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (coronavirus disease 2019 [COVID-19]) pandemic is important for designing prevention and control strategies. Using the New Zealand hospital-based surveillance dataset, we compared the population-based incidence, seasonality, and clinical characteristics of influenza and HMPV infections among hospitalized adults aged 20 years and older with acute respiratory infections (ARI) in Auckland, New Zealand, from 2012 to 2023. In the surveillance project, 37 185 ARI hospitalizations were detected from 2012 to 2023 among adults 20 years and older. Of the 21 649 illnesses tested for HMPV, 735 (3. 4%) were positives and of the 24 138 tested for influenza, 3623 (15. 0%) were positives. Crude rates of annual ARI hospitalizations per 100 000 adult residents were 9. 7 (95% confidence interval [CI], 9-10. 4) for HMPV and 48. 2 (95% CI, 46. 6-49. 7) for influenza. The highest hospitalization rates for both viruses were in those aged 80 years or older, those of Māori or Pacific ethnicity, and those living in low socioeconomic status areas. There were no statistically significant differences in the HMPV-associated ARI hospitalization rates before and after the COVID-19 pandemic. In contrast, influenza-associated hospitalization rates per 100 000 were 43. 0 before the pandemic, increased to 54. 4 in 2022, and then 79. 5 in 2023, with significant increases across most demographic groups. Although HMPV infections accounted for fewer ARI hospitalizations than influenza infections in all study years, relative to younger adults, HMPV-associated ARI hospitalization rates were significantly higher in older adults due to the high prevalence of underlying chronic conditions in this age group. This highlights a need for vaccine/antiviral intervention.

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