Impact of COVID-19 vaccination status on hospitalization and disease severity: A descriptive study in Nagasaki Prefecture, Japan

ABSTRACT

Coronavirus disease 2019 (COVID-19) was extraordinarily harmful, with high rates of infection and hospitalization. This study aimed to evaluate the impact of COVID-19 vaccination status and other factors on hospitalization and disease severity, using data from Nagasaki Prefecture, Japan. Confirmed cases of COVID-19 infection with vaccination status were included and the differences in characteristics between different vaccination statuses, hospitalization or not, and patients with varying levels of disease severity were analyzed. Furthermore, logistic regression was used to calculate odds ratio (ORs) and 95% confidence intervals (CI) to evaluate the association of various factors with hospitalization and disease severity. From March 14, 2020 to August 31, 2022, 23,139 patients were unvaccinated 13,668 vaccinated the primary program with one or two doses, and 4,575 completed the booster. Vaccination reduced the risk of hospitalization with an odd ratio of 0.759 (95% CI: 0.654–0.881) and the protective effect of completed booster vaccination was more pronounced (OR: 0.261, 95% CI: 0.207–0.328). Similarly, vaccination significantly reduced the risk of disease severity (vaccinated primary program: OR: 0.191, 95% CI: 0.160–0.228; completed booster vaccination: OR: 0.129, 95% CI: 0.099–0.169). Overall, unvaccinated, male, elderly, immunocompromised, obese, and patients with other severe illness factors were all risk factors for COVID-19-related hospitalization and disease severity. Vaccination was associated with a decreased risk of hospitalization and disease severity, and highlighted the benefits of completing booster.

KEYWORDS:

• COVID-19
• vaccination
• mRNA vaccine
• Japan
• hospitalization

Acknowledgments

We thank medical personals for checking and reporting the COVID-19 cases.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Abbreviations

COVID-19 Coronavirus disease 2019

WHO World Health Organization

mRNA Messenger RNA

STROBE Strengthening the Reporting of Observational Studies in Epidemiology

VE Vaccine Effectiveness

ORs odds ratio

CKD Chronic Kidney Disease

Author contributions

Conceptualization, Guoxi Cai, Shiwen Liu, Kouichi Morita, Kiyoshi Aoyagi and Fei He; data curation, Guoxi Cai, Yumika Takaki, Fumiaki Matsumoto, Akira Yoshikawa, Toshitsugu Taguri and Maiko Hasegawa; formal analysis, Shiwen Liu, Guoxi Cai, Yixiao LU, Nguyen Tien Huy, Masaya Saito, Shouhei Takeuchi and Fei He; funding acquisition, Guoxi Cai, Taro Yamamoto, Kouichi Morita, Kiyoshi Aoyagi and Fei He; writing – original draft, Shiwen Liu; writing – review and editing, Guoxi Cai, Yixiao LU, Jianfen Xie, Kazuhiko Arima, Satoshi Mizukami, Jiwen Wu and Fei He; All authors have read and agreed to the published version of the manuscript.

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website at https://doi.org/10.1080/21645515.2024.2322795.

Additional information

Funding

This research was funded by the Fujian Provincial Natural Science Foundation Project [No. 2023J01093]. The Major Health Research Project of Fujian Province [No. 2021ZD01001]. The funder of Fujian Provincial Natural Science Foundation Project [No. 2023J01093] is Fei He. The Major Health Research Project of Fujian Province [No. 2021ZD01001] funder is Jianfeng Xie.