Abstract
The study aims to evaluate the association between multiple COVID-19 vaccine doses and daily confirmed cases, incorporating immune response delays to better understand vaccination efficacy. We investigated the effectiveness of multiple COVID-19 vaccinations, with particular emphasis on viral variants, by integrating immune response dynamics into the statistical analysis to provide a more accurate assessment of vaccination outcomes. Detailed data on vaccination numbers and confirmed COVID-19 cases were obtained from the official Korean Ministry of the Interior and Safety website. Multiple linear regression was applied to evaluate the effectiveness of each vaccine dose against different COVID-19 variants. This approach offered a clearer understanding of how vaccination influenced the spread of COVID-19 over time. By accounting for delay periods associated with immune responses, we aimed to provide more accurate insights into the effectiveness of each vaccine dose. The results underscored the impact of multiple vaccinations when incorporating immune response timing and revealed notable differences in the responses of the Delta and Omicron variants to multiple doses. While significant effectiveness was observed against the Omicron variant, a similar positive effect was not evident for the Delta variant.