Negative consequences of failing to communicate uncertainties during a pandemic: an online randomised controlled trial on COVID-19 vaccines

OBJECTIVE: To examine the impact of the government communicating uncertainties relating to COVID-19 vaccine effectiveness on vaccination intention and trust after people are exposed to conflicting information. DESIGN: Experimental design where participants were randomly allocated to one of two groups. SETTING: Online. PARTICIPANTS: 328 adults from a UK research panel. INTERVENTION: Participants received either certain or uncertain communications from a government representative about COVID-19 vaccine effectiveness, before receiving conflicting information about effectiveness. MAIN OUTCOME MEASURES: Vaccination intention and trust in government. RESULTS: Compared with those who received the uncertain announcement from the government, participants who received the certain announcement reported a greater loss of vaccination intention (d=0.34, 95% CI (0.12 to 0.56), p=0.002) and trust (d=0.34, 95% CI (0.12 to 0.56), p=0.002) after receiving conflicting information. CONCLUSIONS: Communicating with certainty about COVID-19 vaccines reduces vaccination intention and trust if conflicting information arises, whereas communicating uncertainties can protect people from the negative impact of exposure to conflicting information. There are likely to be other factors affecting vaccine intentions, which we do not account for in this study. TRIAL REGISTRATION NUMBER: Open Science Framework: https://osf.io/c73px/.