{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,31]],"date-time":"2026-07-31T12:02:16Z","timestamp":1785499336534,"version":"3.56.0"},"reference-count":20,"publisher":"BMJ","issue":"7","license":[{"start":{"date-parts":[[2026,7,31]],"date-time":"2026-07-31T00:00:00Z","timestamp":1785456000000},"content-version":"unspecified","delay-in-days":30,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"funder":[{"DOI":"10.13039\/100010793","name":"Pfizer Japan","doi-asserted-by":"publisher","award":["Not applicable"],"award-info":[{"award-number":["Not applicable"]}],"id":[{"id":"10.13039\/100010793","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Open"],"accepted":{"date-parts":[[2026,7,2]]},"published-print":{"date-parts":[[2026,7]]},"abstract":"<jats:sec>\n                    <jats:title>Introduction<\/jats:title>\n                    <jats:p>Following the reclassification of COVID-19 as a category V infectious disease in Japan in May 2023, systematic public health monitoring of case numbers and cluster outbreaks was discontinued. Consequently, infection control measures, responses to cluster outbreaks and vaccination coverage in long-term care facilities were largely left to the discretion of individual facilities, and the understanding of the current situation in these settings remains insufficient. This observational study aims to retrospectively investigate COVID-19 cluster outbreaks and the resulting burdens experienced by facilities after reclassification, focusing on special nursing homes (Tokubetsu Yogo Rojin Home) for older adults, a population at particularly high risk for COVID-19-associated hospitalisation and mortality. By comprehensively evaluating facility and resident characteristics, vaccination coverage and infection prevention and control measures, this study seeks to generate evidence to inform future infection control strategies in long-term care facilities.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods and analysis<\/jats:title>\n                    <jats:p>\n                      This retrospective observational study targets special nursing homes in Okinawa Prefecture and residents living in these facilities. Data for a target sample of nine nursing homes with approximately 900 residents will be collected from existing facility and medical records using the Research Electronic Data Capture system. The study was initiated in June 2025 and completion is anticipated by March 2027. The primary outcomes are the occurrence of COVID-19 cluster outbreaks in nursing homes between May 2023 and August 2025 and the facility-level burden experienced during outbreaks, including operational and economic impacts. A cluster outbreak is defined as the occurrence of \u22652 cases of the same infectious disease within a 10-day period. Key variables of interest include baseline characteristics of facilities and residents, vaccination coverage among staff and residents and infection prevention and control measures. Additionally, the study explores potential factors associated with residents\u2019 clinical outcomes and facility burden using logistic and linear regression models, respectively, with facility-level random intercepts if deemed appropriate. Prespecified supplementary analyses include one-way analysis of variance and \u03c7\n                      <jats:sup>2<\/jats:sup>\n                      tests.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Ethics and dissemination<\/jats:title>\n                    <jats:p>The study protocol was approved by the Institutional Review Board of the University of the Ryukyus in June 2025 (approval number: 25-2486-00-00-00). The findings will be disseminated at academic conferences and in peer-reviewed medical journals.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1136\/bmjopen-2025-116064","type":"journal-article","created":{"date-parts":[[2026,7,31]],"date-time":"2026-07-31T11:40:21Z","timestamp":1785498021000},"page":"e116064","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":0,"title":["COVID-19 cluster outbreaks and infection control measures in nursing homes in Okinawa: protocol for a retrospective observational study"],"prefix":"10.1136","volume":"16","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-4127-2734","authenticated-orcid":false,"given":"Shuhei","family":"Ideguchi","sequence":"first","affiliation":[{"name":"First Department of Internal Medicine, Division of Infectious, Respiratory, and Digestive Medicine, University of the Ryukyus Graduate School of Medicine, Ginowan, Okinawa, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0008-2029-6730","authenticated-orcid":false,"given":"Yoshihiro","family":"Takayama","sequence":"additional","affiliation":[{"name":"Department of Community Medicine, Okinawa Chubu Hospital, Uruma, Okinawa, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0007-5734-409X","authenticated-orcid":false,"given":"Nanae","family":"Ikemiyagi","sequence":"additional","affiliation":[{"name":"First Department of Internal Medicine, Division of Infectious, Respiratory, and Digestive Medicine, University of the Ryukyus Graduate School of Medicine, Ginowan, Okinawa, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0009-1476-3758","authenticated-orcid":false,"given":"Fuki","family":"Ujimiya","sequence":"additional","affiliation":[{"name":"First Department of Internal Medicine, Division of Infectious, Respiratory, and Digestive Medicine, University of the Ryukyus Graduate School of Medicine, Ginowan, Okinawa, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0009-8825-7743","authenticated-orcid":false,"given":"Kazutaka","family":"Yamaniha","sequence":"additional","affiliation":[{"name":"First Department of Internal Medicine, Division of Infectious, Respiratory, and Digestive Medicine, University of the Ryukyus Graduate School of Medicine, Ginowan, Okinawa, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7995-5250","authenticated-orcid":false,"given":"Miki","family":"Imura","sequence":"additional","affiliation":[{"name":"Vaccine Medical Affairs, Pfizer Japan Inc, Shibuya, Tokyo, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0004-3893-9176","authenticated-orcid":false,"given":"Kosuke","family":"Tanabe","sequence":"additional","affiliation":[{"name":"Vaccine Medical Affairs, Pfizer Japan Inc, Shibuya, Tokyo, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1357-1676","authenticated-orcid":false,"given":"Kazuko","family":"Yamamoto","sequence":"additional","affiliation":[{"name":"First Department of Internal Medicine, Division of Infectious, Respiratory, and Digestive Medicine, University of the Ryukyus Graduate School of Medicine, Ginowan, Okinawa, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"239","published-online":{"date-parts":[[2026,7,31]]},"reference":[{"key":"2026073104400713000_16.7.e116064.1","unstructured":"Ministry of Health, Labour and Welfare . Visualizing the data: information on COVID-19 infections (COVID-19 as of May 7, 2023). 2023. Available: https:\/\/covid19.mhlw.go.jp\/?lang=ja \/ https:\/\/covid19.mhlw.go.jp\/en\/ [Accessed 24 Dec 2025]."},{"key":"2026073104400713000_16.7.e116064.2","unstructured":"Ministry of Health, Labour and Welfare . Trends in the number of reported cases per sentinel site for influenza and COVID-19 (nationwide) [in Japanese]. 2025. 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Updates to COVID-19 epidemiology. Advisory committee on immunization practices. 2025. Available: https:\/\/www.cdc.gov\/acip\/downloads\/slides-2025-09-18-19\/02-Srinivasan-covid-508.pdf [Accessed 24 Dec 2025]."},{"key":"2026073104400713000_16.7.e116064.8","doi-asserted-by":"crossref","first-page":"800","DOI":"10.1016\/j.ajic.2022.09.007","article-title":"High mortality and morbidity among vaccinated residents infected with the SARS-CoV-2 Omicron variant during an outbreak in a nursing home in Kyoto City, Japan","volume":"51","author":"Matsumura","year":"2023","journal-title":"Am J Infect Control"},{"key":"2026073104400713000_16.7.e116064.9","doi-asserted-by":"crossref","DOI":"10.1371\/journal.pone.0309808","article-title":"Clinical features of and severity risk factors for COVID-19 in adults during the predominance of SARS-CoV-2 XBB variants in Okinawa, Japan","volume":"19","author":"Ideguchi","year":"2024","journal-title":"PLoS One"},{"key":"2026073104400713000_16.7.e116064.10","doi-asserted-by":"crossref","DOI":"10.1186\/s41479-025-00158-y","article-title":"Outcomes of COVID-19 in the Omicron-predominant wave: large-scale real-world data analysis with a comparison to influenza","volume":"17","author":"Miyashita","year":"2025","journal-title":"Pneumonia (Nathan)"},{"key":"2026073104400713000_16.7.e116064.11","unstructured":"Ministry of Health, Labour and Welfare . Number of COVID-19 vaccine doses administered during the special temporary vaccination period: results by prefecture [in Japanese]. 2023. Available: https:\/\/www.mhlw.go.jp\/content\/kenbetsu-vaccination_data3.pdf [Accessed 24 Dec 2025]."},{"key":"2026073104400713000_16.7.e116064.12","unstructured":"Ministry of Health, Labour and Welfare . Number of COVID-19 vaccine doses administered during the special temporary vaccination period: results by age group [in Japanese]. 2023. Available: https:\/\/www.mhlw.go.jp\/content\/nenreikaikyubetsu-vaccination_data.pdf [Accessed 24 Dec 2025]."},{"key":"2026073104400713000_16.7.e116064.13","unstructured":"Ministry of Health, Labour and Welfare . Q&amp;A on COVID-19 vaccination: who is eligible for routine (category B) COVID-19 vaccination and what is the vaccination schedule? [in Japanese]. 2024. 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Overview of the 2023 survey of long-term care service facilities and provisions [in Japanese]. 2024. Available: https:\/\/www.mhlw.go.jp\/toukei\/saikin\/hw\/kaigo\/service23\/dl\/gaikyo.pdf [Accessed 24 Dec 2025]."},{"key":"2026073104400713000_16.7.e116064.18","unstructured":"Ministry of Health, Labour and Welfare . Facility- and residential-based long-term care services. The 100th meeting (28 April 2014) - document 4-2 [in Japanese]. 2014. Available: https:\/\/www.mhlw.go.jp\/file\/05-Shingikai-12601000-Seisakutoukatsukan-Sanjikanshitsu_Shakaihoshoutantou\/0000044903.pdf [Accessed 17 Dec 2025]."},{"key":"2026073104400713000_16.7.e116064.19","unstructured":"Ministry of Health Labour and Welfare . Future directions for residential facility for older adults and the role of referral service providers [in Japanese]. 2020. 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