Clinical Report: Impact of HMPV and Influenza Hospitalizations in NZ Adults Pre/Post COVID-19

Overview

This study analyzed hospitalization rates for human metapneumovirus (HMPV) and influenza among adults in Auckland, New Zealand from 2012 to 2023. Influenza hospitalizations increased significantly post-COVID-19 pandemic, whereas HMPV hospitalization rates remained stable. Older adults, Māori and Pacific peoples, and those in lower socioeconomic areas experienced the highest hospitalization rates for both viruses.

Background

Influenza and HMPV are major causes of acute respiratory infections leading to hospitalizations worldwide, particularly affecting older adults and those with chronic conditions. Influenza is well studied with known high morbidity and mortality, while HMPV burden in adults is less defined. Previous studies showed variable HMPV hospitalization rates, often limited by short durations and sampling methods. Understanding temporal trends and the impact of COVID-19 interventions on these viruses is critical for guiding prevention strategies.

Data Highlights

Influenza hospitalization rates increased from 43.0 pre-pandemic to 54.4 in 2022 and 79.5 in 2023 per 100,000 adults. HMPV rates showed no significant change pre- and post-pandemic.

Key Findings

• From 2012 to 2023, 37,185 adult ARI hospitalizations were recorded; 3.4% tested positive for HMPV and 15.0% for influenza.
• Annual crude hospitalization rates per 100,000 adults were 9.7 for HMPV and 48.2 for influenza.
• Hospitalization rates were highest among adults aged ≥80 years, Māori and Pacific ethnicities, and residents of low socioeconomic status areas.
• Influenza hospitalization rates significantly increased post-COVID-19 pandemic, reaching 79.5 per 100,000 in 2023.
• HMPV hospitalization rates remained stable before and after the pandemic with no significant differences.
• Older adults had disproportionately higher HMPV-associated hospitalization rates, likely due to chronic comorbidities, underscoring the need for targeted vaccine or antiviral interventions.

Clinical Implications

Clinicians should be aware of the rising burden of influenza hospitalizations in the post-pandemic period, especially among vulnerable populations such as older adults and indigenous groups. Despite lower overall hospitalization rates, HMPV poses a significant risk to older adults with chronic conditions, highlighting the importance of developing preventive measures including vaccines and antivirals. Surveillance and targeted interventions remain essential to reduce morbidity in high-risk groups.

Conclusion

This extended surveillance study demonstrates a significant post-pandemic increase in influenza hospitalizations among adults in New Zealand, while HMPV hospitalization rates remained stable. The findings emphasize the need for enhanced preventive strategies for both viruses, particularly in older and socioeconomically disadvantaged populations.

References

1. Shaw et al. 2024 -- Assessing the Impact of HMPV and Influenza-Related Hospitalizations in Adults in New Zealand Pre- and Post-COVID-19 Pandemic, 2012–2023