@article{oai:nagasaki-u.repo.nii.ac.jp:00027796,
 author = {Maeda, Haruka and Saito, Nobuo and Igarashi, Ataru and Ishida, Masayuki and Suami, Kazuya and Yagiuchi, Ai and Kimura, Yuya and Komino, Masaru and Arai, Hiromi and Morikawa, Toru and Motohashi, Iori and Miyazawa, Rei and Moriyama, Tetsu and Kamura, Hiroshi and Terada, Mayumi and Kuwamitsu, Osamu and Hayakawa, Tomoichiro and Sando, Eiichiro and Ohara, Yasuji and Teshigahara, Osamu and Suzuki, Motoi and Morimoto, Konosuke},
 issue = {11},
 journal = {Clinical Infectious Diseases},
 month = {Apr},
 note = {Background. Although high vaccine effectiveness of messenger RNA (mRNA) coronavirus disease 2019 (COVID-19) vaccines has been reported in studies in several countries, data are limited from Asian countries, especially against the Delta (B.1.617.2) variant.
Methods. We conducted a multicenter test-negative case-control study in patients aged ≥16 years visiting hospitals or clinics with signs or symptoms consistent with COVID-19 from 1 July to 30 September 2021, when the Delta variant was dominant (≥90% of SARS-CoV-2 infections) nationwide in Japan. Vaccine effectiveness of BNT162b2 or mRNA-1273 against symptomatic SARS-CoV-2 infections was evaluated. Waning immunity among patients aged 16–64 years was also assessed.
Results. We enrolled 1936 patients, including 396 test-positive cases and 1540 test-negative controls for SARS-CoV-2. The median age was 49 years, 53.4% were male, and 34.0% had underlying medical conditions. Full vaccination (receiving 2 doses ≥14 days before symptom onset) was received by 6.6% of cases and 38.8% of controls. Vaccine effectiveness of full vaccination against symptomatic SARS-CoV-2 infections was 88.7% (95% confidence interval [CI], 78.8%–93.9%) among patients aged 16–64 years and 90.3% (95% CI, 73.6%–96.4%) among patients aged ≥65 years. Among patients aged 16–64 years, vaccine effectiveness was 91.8% (95% CI, 80.3%–96.6%) within 1–3 months after full vaccination, and 86.4% (95% CI, 56.9%–95.7%) within 4–6 months.
Conclusions. mRNA COVID-19 vaccines had high effectiveness against symptomatic SARS-CoV-2 infections in Japan during July–September 2021, when the Delta variant was dominant nationwide., Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 75(11), pp.1971-1979; 2022},
 pages = {1971--1979},
 title = {Effectiveness of Messenger RNA Coronavirus Disease 2019 Vaccines Against Symptomatic Severe Acute Respiratory Syndrome Coronavirus 2 Infections During the Delta Variant Epidemic in Japan: Vaccine Effectiveness Real-time Surveillance for SARS-CoV-2 (VERSUS)},
 volume = {75},
 year = {2022}
}