Real-world effectiveness of full and booster mRNA vaccination for coronavirus disease 2019 against disease severity during the delta- and omicron-dominant phases: A propensity score-matched cohort study using the nationwide registry data in Japan

Background: To date, few studies from the Asian region have reported the effectiveness of messenger ribonucleic acid coronavirus disease 2019 (COVID-19) vaccines against disease progression and death after hospitalization. Methods: We evaluated the data from the COVID-19 registry in Japan during the delta- and omicron-dominant phases. A propensity score-matched cohort study was conducted between the incompletely (0–1 dose) and fully (2 doses) vaccinated groups during the delta-dominant phase and among the incompletely, fully, and booster (3 doses) vaccinated groups during the omicron-dominant phase. Results: In the delta-dominant phase, 411 pairs were matched. The fully vaccinated group showed a significantly lower oxygen supplementation rate (24.1 % vs. 41.1 %, p