Progress and challenges in seasonal influenza vaccination across 54 countries and areas in the WHO European Region, 2008/09-2022/23: a repeated cross-sectional ecological study.

Background: Seasonal influenza causes up to 5 million severe cases and 650,000 deaths annually. Vaccination is recommended for high-risk groups and health workers, yet uptake remains low globally. This paper analyses the evolution of seasonal influenza vaccination programmes in the WHO European Region's 54 countries and areas (CA) from 2008/09 to 2022/23 to guide future policy and investment. Methods: We conducted a descriptive, repeated cross-sectional ecological study using national data reported through WHO-UNICEF's Joint Reporting Form on Immunization and reports published by the European Centre for Disease Prevention and Control to analyse influenza vaccine doses, vaccine types, recommendations, coverage, and payment schemes. Trends in doses distributed per capita and older-adult vaccination coverage over 15 seasons were assessed across World Bank income groups. Findings: Since 2008/09, the number of influenza vaccine doses distributed has doubled, driven mainly by increases in upper- (3-fold) and lower-middle-income (8-fold) CA. Yet, by 2022/23, dose availability per 1000 population remained substantially greater in high-income than lower-middle-income settings (145.7 versus 38.5). Recommendations expanded over time to additional target populations, but coverage monitoring remains limited, with fewer than 50% of CA reporting data for key groups, such as health workers. In 2022/23, median coverage among older adults was 55%, and only four CA met the World Health Assembly 75% coverage target. Interpretation: Considerable progress has been made in influenza vaccination across the WHO European Region, with an increasing number of CA recommending vaccination to key target groups. Nonetheless, coverage among priority groups is low, and vaccine supplies vary widely across income levels. Continued investment in national programmes is needed, especially in middle-income CA to keep increasing coverage among high-risk groups. Funding: This work was supported by the Pandemic Influenza Preparedness Framework Partnership Contribution.