Objective
Vaccination is a critical measure for containing the COVID-19 pandemic. We survey the determinants that affect the preference for COVID-19 vaccines in Japan, a vaccine hesitant nation.
Setting
and design
: We conducted a randomized conjoint analysis survey of the preference for vaccines on the Internet by recruiting a nonprobability sample of 15,000 Japanese adults. The survey assigned 5 choice tasks to the respondents. In each task, the respondents evaluated 2 hypothetical COVID-19 vaccines and were asked which they would choose. The vaccine attributes included efficacy, major and minor adverse side effects, country of vaccine development and clinical trial, and vaccine type.
Treatment
The choice task asked the participants to select a vaccine from 2 hypothetical vaccines as an optional vaccine or select a vaccine as a mandatory vaccine with a probability of 0.5 for each.
Results
Compared to vaccines developed in China, vaccines developed domestically or in the US raised the choice probability by 131% and 96%, respectively. A domestic clinical trial increased the choice probability by 33%. An increase in efficacy from 50% to 90% increased the choice probability by 43%. A decrease in the risk of severe side effects from 1 per 10 thousand to 1 per 1 million increased the choice probability by 38%. The vaccine type was irrelevant. Making vaccination compulsory increased the choice probability of China- and Russia-developed vaccines by 6% and 4%, respectively, and increased that of taking a high-risk vaccine by 5% and a modestly effective (70%) vaccine by 4%. General vaccination hesitancy, political positions, demographic characteristics, education, and income were irrelevant.
Conclusions
A domestically developed vaccine with a domestic clinical trial could substantially increase the preference for a vaccine. Making vaccination compulsory could modestly reduce the penalty for a vaccine with side effects, geopolitical, and efficacy concerns.