Among UK adults aged 65 and older enrolled in the FluSurvey participatory surveillance system across two consecutive autumn-winter seasons (2023–2025), receiving one respiratory vaccine was a powerful predictor of receiving the other. Adjusted odds ratios for this cross-vaccine association reached 13.9-fold in 2023–2024, moderating slightly to 8.5-fold in 2024–2025. Influenza uptake held steady at 81% across both seasons, while COVID-19 vaccination rose from 73% to 83%. Lower educational attainment independently reduced COVID-19 vaccination odds by roughly 40–44%, and key barriers included concerns about adverse effects and beliefs in natural immunity.
The magnitude of cross-vaccine clustering is striking and aligns with a well-documented behavioral phenomenon in vaccine research: individuals with pro-vaccine attitudes tend to accept all available vaccines, while hesitancy toward one often generalizes across programs. This "vaccine clustering" effect suggests that outreach strategies targeting hesitant adults could simultaneously improve uptake for multiple pathogens — an efficiency gain with real public health leverage for older, higher-risk populations.
The persistent education gradient in COVID-19 uptake, but not influenza uptake, is worth examining further; it may reflect differential COVID-19 misinformation exposure rather than general vaccine attitudes. Key limitations include the self-selected, volunteer FluSurvey cohort, which likely overrepresents health-engaged adults and may underestimate true barriers in harder-to-reach groups. As a preprint not yet peer-reviewed, these findings require independent validation before informing policy. Overall, this is confirmatory and incremental but provides timely, actionable demographic profiling for seasonal vaccine campaigns.