Evaluating the COVID-19 vaccination program in Japan, 2021 using the counterfactual reproduction number
Abstract Japan implemented its nationwide vaccination program against COVID-19 in 2021, immunizing more than one million people (approximately 1%) a day. However, the direct and indirect impacts of the program at the population level have yet to be fully evaluated. To assess the vaccine effectivenes...
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| Format: | Article |
| Language: | English |
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Nature Portfolio
2023-10-01
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| Series: | Scientific Reports |
| Online Access: | https://doi.org/10.1038/s41598-023-44942-6 |
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| _version_ | 1849226219610963968 |
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| author | Taishi Kayano Yura Ko Kanako Otani Tetsuro Kobayashi Motoi Suzuki Hiroshi Nishiura |
| author_facet | Taishi Kayano Yura Ko Kanako Otani Tetsuro Kobayashi Motoi Suzuki Hiroshi Nishiura |
| author_sort | Taishi Kayano |
| collection | DOAJ |
| description | Abstract Japan implemented its nationwide vaccination program against COVID-19 in 2021, immunizing more than one million people (approximately 1%) a day. However, the direct and indirect impacts of the program at the population level have yet to be fully evaluated. To assess the vaccine effectiveness during the Delta variant (B.1.617.2) epidemic in 2021, we used a renewal process model. A transmission model was fitted to the confirmed cases from 17 February to 30 November 2021. In the absence of vaccination, the cumulative numbers of infections and deaths during the study period were estimated to be 63.3 million (95% confidence interval [CI] 63.2–63.6) and 364,000 (95% CI 363–366), respectively; the actual numbers of infections and deaths were 4.7 million and 10,000, respectively. Were the vaccination implemented 14 days earlier, there could have been 54% and 48% fewer cases and deaths, respectively, than the actual numbers. We demonstrated the very high effectiveness of COVID-19 vaccination in Japan during 2021, which reduced mortality by more than 97% compared with the counterfactual scenario. The timing of expanding vaccination and vaccine recipients could be key to mitigating the disease burden of COVID-19. Rapid and proper decision making based on firm epidemiological input is vital. |
| format | Article |
| id | doaj-art-80f0e26f077e458a948854c697edc4e5 |
| institution | Kabale University |
| issn | 2045-2322 |
| language | English |
| publishDate | 2023-10-01 |
| publisher | Nature Portfolio |
| record_format | Article |
| series | Scientific Reports |
| spelling | doaj-art-80f0e26f077e458a948854c697edc4e52025-08-24T11:31:25ZengNature PortfolioScientific Reports2045-23222023-10-0113111110.1038/s41598-023-44942-6Evaluating the COVID-19 vaccination program in Japan, 2021 using the counterfactual reproduction numberTaishi Kayano0Yura Ko1Kanako Otani2Tetsuro Kobayashi3Motoi Suzuki4Hiroshi Nishiura5Kyoto University School of Public HealthCenter for Surveillance, Immunization, and Epidemiologic Research, National Institute of Infectious DiseasesCenter for Surveillance, Immunization, and Epidemiologic Research, National Institute of Infectious DiseasesKyoto University School of Public HealthCenter for Surveillance, Immunization, and Epidemiologic Research, National Institute of Infectious DiseasesKyoto University School of Public HealthAbstract Japan implemented its nationwide vaccination program against COVID-19 in 2021, immunizing more than one million people (approximately 1%) a day. However, the direct and indirect impacts of the program at the population level have yet to be fully evaluated. To assess the vaccine effectiveness during the Delta variant (B.1.617.2) epidemic in 2021, we used a renewal process model. A transmission model was fitted to the confirmed cases from 17 February to 30 November 2021. In the absence of vaccination, the cumulative numbers of infections and deaths during the study period were estimated to be 63.3 million (95% confidence interval [CI] 63.2–63.6) and 364,000 (95% CI 363–366), respectively; the actual numbers of infections and deaths were 4.7 million and 10,000, respectively. Were the vaccination implemented 14 days earlier, there could have been 54% and 48% fewer cases and deaths, respectively, than the actual numbers. We demonstrated the very high effectiveness of COVID-19 vaccination in Japan during 2021, which reduced mortality by more than 97% compared with the counterfactual scenario. The timing of expanding vaccination and vaccine recipients could be key to mitigating the disease burden of COVID-19. Rapid and proper decision making based on firm epidemiological input is vital.https://doi.org/10.1038/s41598-023-44942-6 |
| spellingShingle | Taishi Kayano Yura Ko Kanako Otani Tetsuro Kobayashi Motoi Suzuki Hiroshi Nishiura Evaluating the COVID-19 vaccination program in Japan, 2021 using the counterfactual reproduction number Scientific Reports |
| title | Evaluating the COVID-19 vaccination program in Japan, 2021 using the counterfactual reproduction number |
| title_full | Evaluating the COVID-19 vaccination program in Japan, 2021 using the counterfactual reproduction number |
| title_fullStr | Evaluating the COVID-19 vaccination program in Japan, 2021 using the counterfactual reproduction number |
| title_full_unstemmed | Evaluating the COVID-19 vaccination program in Japan, 2021 using the counterfactual reproduction number |
| title_short | Evaluating the COVID-19 vaccination program in Japan, 2021 using the counterfactual reproduction number |
| title_sort | evaluating the covid 19 vaccination program in japan 2021 using the counterfactual reproduction number |
| url | https://doi.org/10.1038/s41598-023-44942-6 |
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