The impact of changes in age-based eligibility criteria on seasonal influenza vaccine uptake in England between 2019 and 2024: A retrospective cohort study
Discuss this preprint
Start a discussion What are Sciety discussions?Listed in
This article is not in any list yet, why not save it to one of your lists.Abstract
Objectives
To examine changes in seasonal influenza vaccine uptake among clinical risk groups over periods of differing age-based eligibility.
Design
Retrospective cohort study.
Setting
Individuals in England registered in the Clinical Practice Research Datalink Aurum.
Participants
Between 1,239,802 (2019/20) and 1,289,330 (2023/24) individuals aged 40-69 years in clinical risk groups.
Interventions
Natural experiment involving temporary expansion of age-based eligibility for influenza vaccination to include 50–64-year-olds from 2020/21 to 2022/23.
Main outcome measures
Influenza vaccine uptake from 1 st September to 28 th February, incidence rate ratio (IRR) of vaccine uptake across consecutive seasons within age groups, and the ratio of IRRs between age groups.
Results
Influenza vaccine uptake increased in all age groups in 2020/21 relative to 2019/20. The increase was larger in individuals aged 50-64 years (13.3%; IRR 1.50, 95% CI 1.50-1.51) compared with those aged 40-49 years (8.3%; IRR 1.35, 95% CI 1.34-1.35) and 65-69 years (6.8%; IRR 1.34, 95% CI 1.33-1.35). From 2020/21 to 2022/23, vaccine uptake decreased, with a more pronounced decline among those aged 40-49 years (−5.4%) compared with age-eligible groups (50-64 years: −3.0%; 65-69 years: −3.1%). The reversion of age eligibility in 2023/24 was associated with a larger decrease in uptake among those aged 50-64 years (−9.6% vs 2022/23; IRR 0.79, 95% CI: 0.79-0.79) compared with those aged 40-49 years (−4.9%; IRR 0.87, 95% CI: 0.87-0.88) and 65-69 years (−3.3%; IRR 0.97, 95% CI: 0.96-0.97). Patterns were broadly consistent across clinical risk groups.
Conclusions
The COVID-19 pandemic saw a general increase in seasonal influenza vaccine uptake in clinical risk groups. This increase was larger and more sustained in 50-64 year-olds who had also become eligible based on age. Our findings highlight the potential gains in vaccine coverage among clinical risk groups based on expanded age-based eligibility.
Summary
What is already known on this topic
Seasonal influenza presents a substantial public health burden. Individuals with underlying health conditions have a higher risk of morbidity and mortality from influenza and are eligible for the seasonal influenza vaccine. However, uptake among individuals in clinical risk groups in England remains suboptimal.
What this study adds
We examined whether changes in the age-eligibility threshold for the influenza vaccine from 65 years to 50 years during the COVID-19 pandemic in England (2020/21 to 2022/23) improved uptake among individuals at clinical risk of severe influenza. We found that uptake increased most and was more sustained in 50-64 year-olds who were eligible for vaccination by both age and clinical risk. Our findings highlight the potential gains in vaccine coverage among clinical risk groups based on expanded age-based eligibility.
