Acceptance of vaccines has been on the decline in recent years. Despite encouraging early results for coronavirus vaccine trials, achieving herd immunity requires substantial uptake. We presented scenarios varying vaccine efficacy, minor side effects, and severe reactions to a sample representative of the US population. Vaccine acceptance improved when the efficacy increased beyond 70%. Respondents were unaffected by the probability of minor side effects, such as a sore arm or fever lasting 24 h. The chances of accepting the vaccine were lower when the probability of serious adverse reactions was 1/100,000 in contrast to 1/million or 1/100 million. A replication showed that the results were largely unchanged following the public announcement that the vaccines were 95% effective. All study data are included in the article and/or supporting information.