Impact of Annual Influenza Vaccination on Immune Response in Hong Kong Cohort

Overview

This community-based study in Hong Kong evaluated the effects of repeated annual influenza vaccination on antibody responses during the 2021/22 and 2022/23 seasons. Findings indicate that repeated vaccination is associated with reduced antibody titer increases shortly after vaccination but has minimal impact on antibody levels six months post-vaccination.

Background

Annual influenza vaccination has been recommended since the 1960s to mitigate influenza epidemics. Repeated vaccination can lead to attenuated antibody responses compared to first-time vaccination, potentially reducing vaccine effectiveness. The COVID-19 pandemic halted influenza circulation in Hong Kong from 2020 to early 2023, providing a unique setting to study vaccine-induced immunity without confounding natural infections. This study investigates antibody dynamics and waning in a community cohort receiving repeated influenza vaccinations.

Data Highlights

Key Findings

• Repeated annual influenza vaccination was associated with reduced antibody titer increases at 14 days post-vaccination compared to prior seasons.
• Participants with higher vaccination uptake exhibited significantly slower antibody waning rates against specific vaccine strains.
• Despite slower waning, antibody titers at six months post-vaccination were similar regardless of vaccination history.
• The study leveraged a unique period with no influenza circulation, isolating vaccine-induced antibody responses from infection-induced immunity.
• Hemagglutination inhibition assays were used to measure antibody titers against eight contemporary and two prior vaccine strains.

Clinical Implications

Clinicians should recognize that repeated annual influenza vaccination may lead to lower immediate antibody boosting but does not significantly reduce antibody levels at six months post-vaccination. This supports continued annual vaccination strategies, as long-term antibody persistence remains adequate despite attenuated short-term responses. Monitoring antibody waning can inform optimal timing for vaccination campaigns.

Conclusion

Repeated influenza vaccination in a Hong Kong community cohort results in attenuated early antibody responses but maintains comparable antibody levels at six months post-vaccination. These findings reinforce the value of annual influenza vaccination for sustained immunity.

References

1. EPI-HK Cohort Study, 2023 -- Impact of Annual Influenza Vaccination on Immune Response in a Hong Kong Community Cohort During 2021/22 and 2022/23