Evaluation of the effects of vaccination regimes on the transmission dynamics of COVID-19 pandemic

The COVID-19 pandemic has yet to be eliminated globally despite the advancement of immunization programs. Evaluation of the effects of the vaccination regimes of COVID-19 is critical for understanding the potential capacity of countermeasures and informing subsequent prioritization strategies of responses. Research and observational data provide broad support regarding the importance of effective vaccines, in contrast, debates remain on the timing and priority of booster vaccination under the assumption of resource constraint. This study aims to evaluate the effect of vaccination regimes on the trajectory of the COVID-19 pandemic from the medium-term perspective. We employ a mathematical model to infer critical epidemiological characteristics associated with COVID-19, thereafter perform simulation on the transmission dynamics of the epidemic up to 3 years. The outcomes imply that in the absence of severe variants of the pathogen, administration of booster vaccination curtails the peak size of total cases and share of severe infections at later waves. Nevertheless, it can be better off by prioritizing the primary doses to unvaccinated individuals when vaccine shortage is challenged. The effects of priority categories are consistent across a broad range of profiles. Increasing the rollout capacity (i.e., administration rate) of doses can render the reproduction number lower than one and hence contain the transmission of pandemic ultimately controlling for other factors. The timing of rollout of primary doses is pivotal in reducing the magnitude of transmission saturation. It is of importance to prioritize the administration of primary vaccination series to vulnerable individuals efficiently and thereafter increment of administration capacity when the supply of vaccine increases over time to scale down the size of an epidemic.