Opposing Mechanisms Involving Perceived Benefits versus Safety Partially Explained an Increase in COVID-19 Vaccination Intention among Unvaccinated Chinese Adults during a Post-Rollout Period: Results of Two Serial Surveys

Background: Perceptions related to COVID-19 vaccination are evolving over time, leading to potential changes in vaccination intention among unvaccinated people, which helps in the predictions of vaccination rates. This study investigated the changes in COVID-19 vaccination intention at the population level during a post-rollout period and two potential mechanisms underlying the change via the mediation/suppression effects that involve the perceived benefits/severe side effects of vaccination. Methods: Two serial random population-based telephone surveys interviewed 358 and 145 Chinese adults (aged 18–70) who were unvaccinated and who were unscheduled for COVID-19 vaccination, respectively, in May and August 2021 in Hong Kong, China. Results: The prevalence of vaccination intention increased from 14.5% to 22.8%, while the levels of perceived benefits (protection and travel-related advantages due to vaccination) and the perceived risk of severe side effects resulting from COVID-19 vaccination both significantly declined over time. Structural equation modeling found a simultaneous partial suppression effect via perceived benefits and a partial mediation effect via perceived severe side effects between the time when the surveys were conducted and COVID-19 vaccination intention, with adjustment for background factors. Conclusion: Perceptions related to COVID-19 vaccination are likely to change over time and partially account for changes in vaccination intention, sometimes in opposite directions. Ongoing health promotion may take such changes into account. Serial surveillance is warranted to monitor these changes.