Testing an extended theory of planned behaviour in predicting Covid-19 vaccination intention over the course of the pandemic: A three-wave repeated cross-sectional study

Background: Mass vaccination against Covid-19 has been recognised as the most effective strategy for overcoming the pandemic emergency and remains crucial in the ongoing efforts to mitigate the impact of the virus. The present study aimed to test the efficacy of an extended Theory of Planned Behaviour (TPB) model in predicting vaccination intention in three different phases of the pandemic. Understanding how psychological drivers of vaccine acceptance may have changed throughout the pandemic is essential for informing public health strategies and addressing vaccine hesitancy, even in the current post-pandemic context. Methods: Using a repeated cross-sectional survey, we tested the hypothesised extended TPB model (intention, attitude, subjective norms, perceived behavioural control, anticipated affective reactions, risk perception, trust in science, trust in institutions and religiosity) across three independent samples: before (T1: November-December 2020; N = 657), during (T2: March-May 2021; N = 818), and after (T3: February-March 2022; N = 605) the start of the vaccination campaign in Italy. Results: Results indicated significant differences between the time points in all investigated variables, pointing to a general trend of improvement in vaccine acceptability levels at T2 compared to T1, and a worsening at T3 compared to the other two time points. Interestingly, net of these differences, a multi-group Structural Equation Modeling analysis supported the invariance, across time, of the structural relationships examined within the extended TPB. Conclusion: Findings demonstrated the efficacy of the TPB in predicting Covid-19 vaccination intention at different stages of the pandemic, suggesting that the model, in its extended version, represents a valuable framework for designing interventions aimed at promoting vaccine acceptance.