Effects of age-based eligibility changes on influenza vaccine uptake in England, 2019–2024

Abstract Seasonal influenza presents a significant burden on the healthcare system, especially among individuals with underlying health conditions. In England, an annual influenza vaccine is recommended for high-risk individuals (those aged 65 and over, and those aged 18-64 in clinical risk groups). The vaccine eligibility was temporarily expanded during the COVID-19 pandemic to include all adults aged 50 years and over during the 2020/21 to 2022/23 seasons. This study aimed to assess the impact of this expanded age eligibility on vaccine uptake among individuals in clinical risk groups. We conducted a retrospective cohort study using English primary care data (CPRD Aurum), covering influenza seasons 2019/20-2023/24. The study included individuals aged 40-69 years with chronic conditions eligible for vaccination per national guidelines. Vaccination status was determined from health records for each season (1 September to 28 February). Multivariate log-binomial regression with robust standard errors was used to compare uptake ratios between seasons and age groups. Vaccine uptake ranged from 57.23% (in 2023/24) to 68.88% (in 2020/21), with the highest uptake in individuals with immunosuppression and the lowest in those with a BMI over 40 kg/m². Vaccine uptake increased in all age groups, with a relative risk (RR) for vaccination in 2020/21 compared to 2019/20 of 1.18 (95% CI: 1.17-1.18) for those aged 40-49 years, 1.21 (95% CI: 1.21-1.21) for 50-64 year-olds, and 1.08 (95% CI: 1.08-1.08) for 65-69 year-olds. The 50-64 age group showed the greatest increase in uptake when eligibility expanded, with a higher ratio of RR compared to the other age groups. The first autumn/winter of the COVID-19 pandemic (2020/21) saw a general increase in seasonal influenza vaccine uptake in clinical risk groups, with the most significant increase observed in individuals aged 50-64 who had also become eligible based on age. This pattern was consistent across different underlying health conditions. Key messages • Influenza vaccine uptake has improved in all individuals aged 40-69 years in clinical risk groups at the start of the COVID-19 pandemic but most in those aged 50-64. • Being eligible for the influenza vaccine by age and underlying health condition can improve uptake in comparison to being eligible by underlying health condition alone in the context of a pandemic.