{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,21]],"date-time":"2026-07-21T15:23:10Z","timestamp":1784647390467,"version":"3.55.0"},"reference-count":45,"publisher":"PeerJ","license":[{"start":{"date-parts":[[2022,1,19]],"date-time":"2022-01-19T00:00:00Z","timestamp":1642550400000},"content-version":"unspecified","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Health and Labor Sciences Research","award":["19HB1001, 19HA1003, 20CA2024, 20HA2007, and 21HB1002 to H.N"],"award-info":[{"award-number":["19HB1001, 19HA1003, 20CA2024, 20HA2007, and 21HB1002 to H.N"]}]},{"DOI":"10.13039\/100009619","name":"Japan Agency for Medical Research and Development","doi-asserted-by":"crossref","award":["JP20fk0108140 and JP21fk0108612 to H.N"],"award-info":[{"award-number":["JP20fk0108140 and JP21fk0108612 to H.N"]}],"id":[{"id":"10.13039\/100009619","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science KAKENHI","doi-asserted-by":"crossref","award":["A.S: 19K24159, H.N: 17H04701 and 21H03198"],"award-info":[{"award-number":["A.S: 19K24159, H.N: 17H04701 and 21H03198"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100003844","name":"Inamori Foundation","doi-asserted-by":"crossref","id":[{"id":"10.13039\/501100003844","id-type":"DOI","asserted-by":"crossref"}]},{"name":"GAP Fund Program of Kyoto University"},{"name":"Japan Science and Technology Agency CREST program","award":["JPMJCR1413 to H.N"],"award-info":[{"award-number":["JPMJCR1413 to H.N"]}]},{"name":"SICORP program","award":["JPMJSC20U3 and JPMJSC2105 to H.N"],"award-info":[{"award-number":["JPMJSC20U3 and JPMJSC2105 to H.N"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>In Japan, routine two-dose immunization against varicella has been conducted among children at ages of 12 and 36 months since 2014, and the vaccination coverage has reached around 90%. To understand the impact of routine varicella vaccination, we reconstructed the epidemiological dynamics of varicella in Japan.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>Epidemiological and demographic datasets over the past three decades were analyzed to reconstruct the number of susceptible individuals by age and year. To estimate the annual risk of varicella infection, we fitted a balance equation model to the annual number of cases from 1990 to 2019. Using parameter estimates, we reconstructed varicella dynamics starting from 1990 and modeled future dynamics until 2033.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Overall varicella incidence declined over time and the annual risk of infection among children younger than 10 years old decreased monotonically starting in 2014. Conversely, varicella incidence among teenagers (age 10 to 14 years) has increased each year since 2014. A substantial number of unvaccinated individuals born before the routine immunization era remained susceptible and aged without contracting varicella, while the annual risk of infection among teenagers aged 10 to 14 years increased starting in 2011 despite gradual expansion of varicella vaccine coverage. The number of susceptible individuals decreased over time in all age groups. Modeling indicated that susceptibility rates among pre-school children aged 1 to 4 years will remain low.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>Routine varicella vaccination has successfully reduced infections in pre-school and early primary school age children, but has also resulted in increased infection rates among adolescents. This temporary increase was caused both by the increased age of susceptible individuals and increased transmission risk among adolescents resulting from the dynamic nature of varicella transmission. Monitoring susceptibility among adolescents will be important to prevent outbreaks over the next decade.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.7717\/peerj.12767","type":"journal-article","created":{"date-parts":[[2022,1,19]],"date-time":"2022-01-19T05:15:01Z","timestamp":1642569301000},"page":"e12767","source":"Crossref","is-referenced-by-count":11,"title":["Reconstructing the transmission dynamics of varicella in Japan: an elevation of age at 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