Applying two behavioral theories to predict the willingness to receive COVID-19 vaccine booster in the elderly: A cross-sectional study

Background: The COVID-19 vaccination booster can effectively protect the elderly from infection while also lowering the risk of serious illness and death. However, barriers remain in willingness of the elderly to boost vaccination.Objective: Using the protection motivation theory (PMT) and the theory of planned behavior (TPB), to study the factors that influence willingness of the elderly to get the COVID-19 vaccine booster. Methods: The elderly who visited three randomly selected medical institutions in Nanjing's core urban region between March and April 2022 were chosen as study participants. A face-to-face survey was conducted using purposeful sampling and a self-designed questionnaire. The questionnaire contained sociodemographic charac-teristics, the elderly's willingness to obtain a COVID-19 vaccine booster, and psychosocial cognitive components based on the PMT and TPB. SmartPLS 3.0 was used to conduct structural equation modeling.Results: 214 participants were included in the analysis. The combined model of the two behavioral theories explained the willingness to accept COVID-19 vaccine booster well with R2 of 0.490. Self-efficacy (fl = 0.315) was the strongest predictor of vaccine booster willingness. Subjective norms (fl = 0.160), perceived severity (fl = 0.157), and perceived vulnerability (fl = 0.159) also showed positive effects on vaccine booster willingness, while response cost (fl =-0.143) had a negative effect on the willingness. No significant association between attitudes, response efficacy and the willingness was discovered.Conclusion: The willingness of the elderly to receive the COVID-19 vaccine booster was affected by psychosocial cognitive factors. This study supports the applicability of the PMT and TPB models to interpret the willingness of the elderly in such areas.