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Aim: Western Australian laboratory data demonstrated a decrease in human metapneumovirus (hMPV) detections through 2020 associated with SARS‐CoV‐2‐related non‐pharmaceutical interventions (NPIs), followed by a subsequent surge in metropolitan region in mid‐2021. We aimed to assess the impact of the surge in hMPV on paediatric hospital admissions and the contribution of changes in testing. Methods: All respiratory‐coded admissions of children aged <16 years at a tertiary paediatric centre between 2017 and 2021 were matched with respiratory virus testing data. Patients were grouped by age at presentation and by ICD‐10 AM codes into bronchiolitis, other acute lower respiratory infection (OALRI), wheeze and upper respiratory tract infection (URTI). For analysis, 2017–2019 was utilised as a baseline period. Results: hMPV‐positive admissions in 2021 were more than 2.8 times baseline. The largest increase in incidence was observed in the 1–4 years group (incidence rate ratio (IRR) 3.8; 95% confidence interval (CI): 2.5–5.9) and in OALRI clinical phenotype (IRR 2.8; 95% CI: 1.8–4.2). The proportion of respiratory‐coded admissions tested for hMPV in 2021 doubled (32–66.2%, P < 0.001), with the greatest increase in wheeze (12–75% in 2021, P < 0.001). hMPV test percentage positivity in 2021 was higher than in the baseline period (7.6% vs. 10.1% in 2021, P = 0.004). Conclusion: The absence and subsequent surge underline the susceptibility of hMPV to NPIs. Increased hMPV‐positive admissions in 2021 can be partially attributable to testing, but test‐positivity remained high, consistent with a genuine increase. Continued comprehensive testing will help ascertain true burden of hMPV respiratory diseases. [ABSTRACT FROM AUTHOR]

Non-pharmaceutical interventions (NPIs) to reduce SARS-CoV-2 transmission disrupted respiratory virus seasonality. We examined the unusual return of human metapneumovirus (hMPV) in Western Australia following a period of absence in 2020. We analysed hMPV laboratory testing data from 1 January 2017 to 31 December 2021. Whole-genome sequencing of selected hMPV-positive samples was performed using a tiled-amplicon approach. Following an absence in spring 2020, an unusual hMPV surge was observed during the wet summer season in the tropical Northern region in late 2020. Following a six-month delay, an intense winter season occurred in the subtropical/temperate Southern and Metropolitan regions. Compared to 2017–2019, hMPV incidence in 2021 increased by 3-fold, with a greater than 4-fold increase in children aged 1–4 years. There was a collapse in hMPV diversity in 2020, with the emergence of a single subtype. NPIs contributed to an absent 2020 season and a clonal hMPV resurgence. The summer surge and delayed winter season suggest that prevailing temperature and humidity are keys determinant of hMPV transmission. The increased incidence in 2021 was linked to an expanded cohort of hMPV-naïve 1–4-year-old children and waning population immunity. Further intense and unusual respiratory virus seasons are expected as COVID-19 associated NPIs are removed. [ABSTRACT FROM AUTHOR]