{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,29]],"date-time":"2026-01-29T03:40:08Z","timestamp":1769658008131,"version":"3.49.0"},"reference-count":43,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2026,1,28]],"date-time":"2026-01-28T00:00:00Z","timestamp":1769558400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100009619","name":"Japan Agency for Medical Research and Development","doi-asserted-by":"publisher","award":["JP24fk0108709"],"award-info":[{"award-number":["JP24fk0108709"]}],"id":[{"id":"10.13039\/100009619","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Children"],"abstract":"<jats:p>Background\/Objectives: Evidence regarding the impact of COVID-19 vaccination on children and adolescents remains limited, particularly in Japan. Thus, this study aimed to estimate incidence rates of COVID-19-associated hospitalization by vaccination status and evaluate the association between COVID-19 vaccination and COVID-19-associated hospitalization among individuals aged 6 months to &lt;18 years in Japan. Methods: We conducted a retrospective, population-based cohort study using linked health insurance claims data and municipal COVID-19 vaccination registry records from nine Japanese municipalities between 1 January 2022, and 31 March 2023, when the Omicron variant was dominant nationwide. Incidence rates of COVID-19-associated hospitalization were estimated among unvaccinated individuals and those who had received one dose (partially vaccinated) or at least two doses of an ancestral monovalent COVID-19 vaccine (fully vaccinated). Incidence rate ratios (IRRs) were calculated, adjusting for age group, sex, presence of underlying medical conditions, municipality, and calendar month. Results: Among 163,305 individuals, 93 COVID-19-associated hospitalizations were identified. Crude incidence rates were 4.5 (95% confidence interval [CI]: 3.6\u20135.6), 3.2 (95% CI: 0.1\u201318.0), and 2.3 (95% CI: 1.1\u20134.2) per 100,000 person-months in unvaccinated, partially, and fully vaccinated groups, respectively. The adjusted IRR for the fully vaccinated group was 0.429 (95% CI: 0.198\u20130.930). Among hospitalized patients, 30.1% had underlying medical conditions, and only 4.3% required oxygen administration during hospitalization. Conclusions: Receiving at least two doses of COVID-19 vaccine was associated with a lower incidence rate of COVID-19-associated hospitalization among children and adolescents during the Omicron-dominant period in Japan. Expanding vaccine uptake among eligible pediatric populations may help reduce the burden of severe disease.<\/jats:p>","DOI":"10.3390\/children13020183","type":"journal-article","created":{"date-parts":[[2026,1,28]],"date-time":"2026-01-28T15:04:46Z","timestamp":1769612686000},"page":"183","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Incidence of COVID-19-Associated Hospitalization by Vaccination Status in Children and Adolescents During Omicron-Dominant Period in Japan: The VENUS Study"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0014-2602","authenticated-orcid":false,"given":"Haruka","family":"Maeda","sequence":"first","affiliation":[{"name":"Department of Respiratory Infections, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8401-9344","authenticated-orcid":false,"given":"Michiko","family":"Toizumi","sequence":"additional","affiliation":[{"name":"Department of Pediatric Infectious Diseases, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ataru","family":"Igarashi","sequence":"additional","affiliation":[{"name":"Department of Health Policy and Public Health, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Megumi","family":"Maeda","sequence":"additional","affiliation":[{"name":"Department of Health Care Administration and Management, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Futoshi","family":"Oda","sequence":"additional","affiliation":[{"name":"Department of Health Care Administration and Management, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Haruhisa","family":"Fukuda","sequence":"additional","affiliation":[{"name":"Department of Health Care Administration and Management, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,28]]},"reference":[{"key":"ref_1","unstructured":"Ministry of Health, and Labour and Welfare (2025, November 22). 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