OCEAN.

Study characteristics
Methods	Study design: randomised controlled trial Type of publication: journal publication Setting and dates: online, Jan 19 to Feb 5, 2021 Country: UK Language: English
Interventions	Control condition 1: Safety and effectiveness statement taken from the NHS website Condition 2: Adding the collective vaccination benefit of not personally getting ill Condition 3: Adding the collective vaccination benefit of not transmitting the virus to others Condition 4: Adding the collective vaccination benefits of not getting ill and not transmitting the virus (i.e.combining conditions 2 and 3) Condition 5: Adding the personal benefit of getting vaccinated Condition 6: Adding the seriousness of the pandemic (and that it is much more serious than seasonal influenza) Condition 7: Directly addressing concerns about vaccine safety related to the speed of development Condition 8: Indirectly addressing concerns about vaccine safety related to the speed of development Condition 9: Adding the collective and personal benefits together (i.e. combining conditions 4 and 5) Condition 10: Adding the information on the collective and personal benefits, the seriousness of the virus, and the information that indirectly addresses concerns about the speed of development (i.e. combining conditions 4, 5, 6, and 8)
Population	Age: 43.2 (18.1) Gender: 55.8% Female, 43.3% Male, 0.5% non‐binary, 0.5% prefer not to say Ethnicity: 81% White, 3.8% multiple ethic groups, 7.3% Asian or Asian British, 5.5% Black, African, Caribbean, or Black British, 2.4% Other ethnic group Number of participants (recruited/allocated/evaluated): 18 855 Inclusion/exclusion criteria: UK adults (≥18 years of age)
Outcomes	Primary outcome:  Willingness to be vaccinated, as measured by the Oxford COVID‐19 Vaccine Hesitancy Scale
Notes	Funding: NIHR Oxford Biomedical Research Centre and the NIHR Oxford Health Biomedical Research Centre. COI: AJP is Chair of UK Department Health and Social Care's Joint Committee on Vaccination & Immunisation, but does not participate in discussions on COVID‐19 vaccines, and is a member of the WHO's SAGE. Oxford University has entered into a partnership with AstraZeneca for the development of a coronavirus vaccine. All other authors declare no competing interests..