Background <p>Timely vaccination effectively reduced COVID-19 hospitalizations and mortality, yet vaccination hesitancy undermined this benefit. Understanding the factors contributing to hesitancy is critical for improving future pandemic control by identifying barriers to timely vaccination. This paper operationalizes hesitancy in terms of vaccine delay—a key public health metric that reflects changing vaccination policies and infection status, factors that can alter individuals’ eligibility, and real-world complexities like infections.</p> Method <p>Using longitudinal data from the earliest stage of the pandemic in Hong Kong, we examined how institutional trust and the 5C constructs (confidence, complacency, constraints, calculation, and collective responsibility) influenced both vaccination intention and timing.</p> Results <p>Our results show that only 34.89% and 42.97% of vaccinated participants received their first and third doses within 100 days of eligibility, respectively, despite rising uptake prior to government mandates. Confidence and vaccination intention are key predictors of delay, and higher institutional trust boosts both confidence and collective responsibility, thereby enhancing intention and reducing delays.</p> Conclusions <p>These findings underscore the importance of building institutional trust and public confidence to minimize vaccine delay, particularly among vulnerable populations. Ultimately, incorporating vaccine delay as a key metric into public health strategies can guide more effective interventions and strengthen pandemic preparedness.</p>