How to boost the boosters? A survey-experiment on the effectiveness of different policies aimed at enhancing acceptance of a "Seasonal" vaccination against COVID-19.

Background: Evidence suggests a gradual decrease in the effectiveness of the anti-COVID-19 vaccines, stressing the potential need for periodical booster shots. However, it is hard to tell whether previously applied policies for enhancing vaccine acceptance will be as effective for repeated periodical booster shots during a pandemic. Hence, this study aims to explore the effectiveness of different health policies on periodical vaccination acceptance amidst an ongoing pandemic.

Methods: A cross sectional online experiment was performed in a representative sample of 929 Israeli citizens. Participants were randomly allocated to 4 groups simulating different hypothetical periodical-vaccination-promoting policy scenarios: (1) Mandate (N = 229); (2) a negative monetary incentive (N = 244); (3) a positive monetary incentive (N = 228) and (4) information provision (N = 228). Compliance intentions and vaccine-acceptance-related variables were measured. Analysis included multivariate hierarchic logistic and linear regressions.

Results: Compliance intentions levels were medium (M = 3.13 on a 1-5 scale). Only 20.2% of the sample demonstrated strong acceptance of periodical vaccination, which is lower than the acceptance rate of the seasonal flu shot in the country in the year preceding the pandemic. Type of policy was related to the extent to which a respondent strongly agreed to be periodically vaccinated or not. Specifically, strong acceptance was more likely when positive or negative incentives were presented in comparison to the mandate or information provision conditions. However, when examining the extent of compliance among respondents who were less decisive, the type of policy did not predict the extent to which these respondents intended to comply. In addition, compliance intentions were related with the perceived benefits and barriers of the vaccine, the perceived efficacy of getting vaccinated and social norms. Hesitator's intentions were additionally associated with anti-COVID-19 vaccination history, perceived severity of the disease and trust in government.

Conclusions: Pandemic-containing vaccines may be perceived as less effective and beneficial than pandemic-preventing vaccines. Individuals with different levels of motivation for periodical vaccination during a pandemic may be affected by different factors. While strongly opinionated individuals are affected by the type of vaccination-promoting policy, hesitators are affected by a larger number of factors, which provide policy makers with greater opportunities to enhance their vaccination intentions.