The impact of the COVID-19 pandemic on healthy volunteer motivations: a mixed-methods study of participants in plague vaccine trials in the UK and Uganda

Background The COVID-19 pandemic led to unprecedented interest and participation in vaccine trials globally, and a concurrent increase in vaccine hesitancy. Whether this impacted recruitment of healthy volunteers to subsequent non-COVID vaccine trials is not well studied. We explored the impact of the COVID-19 pandemic on motivations for participating in two clinical trials of the same novel anti-plague vaccine, conducted in the United Kingdom (UK) and Uganda in 2021 and 2022. Methods Participants enrolled in PlaVac (UK) and PlaVac Uganda, Phase I trials of ChAdOx1 Plague vaccine, were invited to complete an optional questionnaire and semi-structured interview examining motivations for participating, including questions on the impact of the COVID-19 pandemic on their decision. Questionnaires were self-administered and interviewer-administered for UK and Uganda studies, respectively. Interviews were conducted in local languages, transcribed in English, and analysed using thematic analysis. Results were compared between studies. Results Thirty-one of the 45 (25.8% female) UK trial participants and all 36 (27.8% female) of the Uganda trial participants completed questionnaires. Nine UK questionnaire respondents, and 19 Uganda questionnaire respondents completed interviews. Responses to questions on the impact of the COVID-19 pandemic on volunteering decisions were divergent between countries, with little effect for UK participants but a strong positive effect for Ugandan participants. Themes relating to this effect in Uganda were preparedness (wanting to contribute to vaccine development to prevent suffering and death from future epidemics), increased awareness (understanding the vaccine development process and seeing rapidly deployed COVID-19 vaccine trials gave them confidence), and personal protection (believing themselves to be protected by the novel plague vaccine). Participants in both studies expressed trust and confidence in the study plague vaccine which shares the ChAdOx1 platform with the ChAdOx1 nCoV-19 (Vaxzevria, AstraZeneca) vaccine. Conclusions For Ugandan participants, COVID-19 and mass vaccination increased knowledge about vaccines and trials and encouraged them to participate in research, but had little impact on UK volunteers. There was no evidence of a negative effect of perceptions of the related ChAdOx1 nCoV-19 vaccine on trial participants' confidence in the novel plague vaccine's safety. Trial registrations Current controlled trial: ISRCTN41077863, prospective registration date: 19/03/2021, and current controlled trial: ISRCTN79243381, prospective registration date 05/08/2022.