Evaluating COVID-19 vaccination policy in Québec (Canada) using a data-driven dynamic transmission model

Area of Science:

• Epidemiology
• Mathematical Modeling
• Public Health Policy

Background:

• COVID-19 pandemic presented decision-makers with imperfect information and resource constraints, potentially leading to non-optimal public health interventions.
• Vaccine availability and rollout strategies significantly influenced disease burden during the pandemic.
• Understanding the impact of different vaccination prioritization sequences is crucial for effective pandemic response.

Purpose of the Study:

• To perform counterfactual evaluations of various vaccination strategies on COVID-19 burden in Québec.
• To assess the effect of alternative age-specific vaccine prioritization sequences.
• To evaluate the impact of vaccine hesitancy on the effectiveness of different vaccination strategies.

Main Methods:

• Development and calibration of a deterministic, compartmental dynamic transmission model stratified by age, susceptibility, variant, and immunity.
• Utilizing population-based surveillance data and Approximate Bayesian Computation Sequential Monte Carlo (ABC-SMC) for parameter estimation.
• Performing counterfactual analyses to compare different vaccination prioritization strategies and vaccine uptake scenarios.

Main Results:

• The implemented strategy of prioritizing highest-risk age groups was only marginally outperformed by prioritizing younger, socially connected groups and individuals aged 50+ (3% fewer hospitalizations).
• Optimal strategies generally showed fewest hospitalizations at highest vaccine uptake rates, but sub-optimal strategies could increase hospitalizations with higher uptake due to dose redistribution.
• Findings demonstrate that vaccination strategy impact is contingent on population factors like contact patterns, vaccine uptake, and immunity levels.

Conclusions:

• Vaccination prioritization policies significantly influence COVID-19 burden, with nuanced effects depending on population characteristics and vaccine hesitancy.
• The study underscores the importance of considering social connectivity and age-specific risks when designing vaccine rollout strategies.
• These insights are vital for informing future public health decisions for emerging pathogens and potential vaccine shortages.