Effects of booster vaccination on post-treatment oxygen deterioration in hospitalized mild-to-moderate COVID-19 Japanese patients with comorbidities during the Omicron wave

Introduction: Although the emergence of the Omicron variant has decreased overall mortality from Coronavirus Disease 2019 (COVID-19) compared to the Delta variant, elderly individuals with comorbidities remain at increased risk of adverse outcomes. While vaccination and antiviral treatments have reduced the severity of COVID-19, data on the impact of booster vaccination on post-hospitalization oxygen deterioration in the Japanese population remain limited. Methods: We conducted a retrospective study of hospitalized mild-to-moderate COVID-19 Japanese patients during the Omicron variant wave (December 2021 to October 2022). Both vaccinated and unvaccinated patients were included and categorized into three groups based on their vaccination status: unvaccinated (0–1 vaccine dose), primary series (2 vaccine doses), and booster group (3–4 vaccine doses). Demographic and clinical data were collected, and the frequency and time to post-hospitalization oxygen deterioration were evaluated among the three groups. Results: A total of 596 patients were analyzed (141 unvaccinated, 180 primary series, and 275 booster group). The booster group showed significantly lower rates of oxygen deterioration and a longer time to deterioration compared to the other groups, despite being older and having more comorbidities. A multivariate analysis, adjusted for age and gender, revealed that booster vaccination was significantly associated with a reduced risk of oxygen deterioration after initial treatment. Similar results were observed in the subgroup analysis of elderly patients aged 65 years and older. Conclusion: Our study demonstrated the effectiveness of booster vaccination on preventing post-treatment oxygen deterioration in hospitalized mild-to-moderate COVID-19 Japanese patients with comorbidities during the Omicron wave.