Vaccination behavior under uncertainty: a longitudinal study on factors associated with COVID-19 vaccination behavior in Japan with a focus on the effect of close contacts’ vaccination behavior

Objective While apprehension and uncertainty toward the newly developed COVID-19 vaccines may be natural, it is crucial to encourage vaccination to manage the pandemic effectively. This study aimed to examine how beliefs, attitudes, and changes in the vaccination behavior of close contacts from the beginning of vaccine distribution predict COVID-19 vaccination behavior approximately one year later in a Japanese sample.Method A longitudinal web-based survey was conducted at three points between May 14–16, 2021, and August 12–18, 2022. By the third time point, 1,046 participants (mean age = 48.81, SD = 14.07, range = 20–80) had completed the survey.Results By time 3, 73% of participants had received three or more shots. Ordinal logistic regression revealed that the initial responses to the questions ‘Do you know anyone close to you who got vaccinated for COVID-19?’ and ‘Do you know anyone close to you who is saying they will not get vaccinated for COVID-19?’ were the most significant predictors of later vaccination behavior, even when accounting for other factors such as attitudes toward and knowledge of COVID-19.Conclusions The findings suggest that, irrespective of individual attitudes toward vaccines, the initial vaccination behavior of close contacts strongly influences an individual’s vaccination behavior one year and three months later. These results provide valuable insights into vaccination behavior amidst significant uncertainty.