COVID-19 vaccine uptake varied across countries, in part due to vaccine hesitancy fueled by a lack of trustworthy information. To help health workers provide evidence-based answers to common questions about COVID-19 vaccines and vaccination, and thereby, assist individuals´ decisions on vaccine acceptance, COVID-19 InfoVaccines, a joint WHO-EU project, was launched in February 2021 to support COVID-19 vaccine rollout in 6 Eastern European countries. COVID-19 InfoVaccines was made available in seven languages and shared on social media networks. A total of 262,592 users accessed COVID-19 InfoVaccines.com between February 11, 2021, and January 31st, 2023. The users were most interested in: general questions; vaccine efficacy and duration of protection; vaccine safety; vaccine co-administration, and dose-interval and interchangeability; though the interest in a specific theme varied in function of the epidemiological situation. A total of 118,510 (45.1%) and 46,644 (17.7%) users scrolled up to 35% and 75% of the COVID-19 InfoVaccines webpage, respectively. The average engagement rate was 71.61%. The users accessed COVID-19 InfoVaccines from 231 countries and territories, but the majority were in Ukraine (N = 38,404; 14.6%), Spain (N = 23,327; 8.9%), and Argentina (N = 21,167; 8.1%). Older Facebook users were more interested in COVID-19 information than younger individuals (X2 p-value < .0001). Two hundred twenty-eight videos were shared on YouTube. The average Click-Through-Rate on Facebook was 7.82%, and that on YouTube was 4.4%, with 60 videos having a Click-Through-Rate >5%, falling in the range of average YouTube video Click-Through-Rate (2% - 10%). As misinformation about vaccines and vaccination spreads easily and can negatively impact health-related decisions, initiatives like COVID-19 InfoVaccines are crucial to facilitate access to reliable information.

Centro de Investigación Biomédica en Red de Enfermedades Respiratorias Instituto de Salud Carlos 3 Madrid Spain

Centro de Investigación Biomédica en Red de Epidemiología y Salud Pública Madrid Spain

Department of Preventive Medicine University of Santiago de Compostela Santiago de Compostela Spain

Digital Marketing Consultant and Project Manager World Health Organization Georgia

English Russian medical interpreter translator Russian Federation

Genetics Vaccines and Pediatric Infectious Diseases Research Group Instituto de Investigación Sanitaria de Santiago de Compostela Santiago de Compostela Spain

Head of Design and Development Marketing agency Sisuco Solutions Madrid Spain

Servicio de Medicina Preventiva y Salud Pública Hospital Vital Álvarez Buylla Asturias Spain

Translational Pediatrics and Infectious Diseases Hospital Clínico Universitario de Santiago de Compostela and USC Santiago de Compostela Spain

WHO Collaborating Centre for Vaccine Safety Santiago de Compostela Spain

World Health Organization Country Office Bucharest Romania

World Health Organization Country Office Czechia

World Health Organization Country Office in Ukraine Kyiv Ukraine

World Health Organization Regional Office for Europe Copenhagen Denmark

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