@article{oai:nagasaki-u.repo.nii.ac.jp:00027923,
 author = {Arashiro, Takeshi and Arima, Yuzo and Muraoka, Hirokazu and Sato, Akihiro and Oba, Kunihiro and Uehara, Yuki and Arioka, Hiroko and Yanai, Hideki and Kuramochi, Jin and Ihara, Genei and Chubachi, Kumi and Yanagisawa, Naoki and Nagura, Yoshito and Kato, Yasuyuki and Ueda, Akihiro and Numata, Akira and Kato, Hideaki and Ishii, Koji and Ooki, Takao and Oka, Hideaki and Nishida, Yusuke and Stucky, Ashley and Smith, Chris and Hibberd, Martin and Ariyoshi, Koya and Suzuki, Motoi},
 issue = {3},
 journal = {Clinical Infectious Diseases},
 month = {Feb},
 note = {Background. Although several coronavirus disease 2019 (COVID-19) vaccines initially showed high efficacy, there have been concerns because of waning immunity and the emergence of variants with immune escape capacity.
Methods. A test-negative design case-control study was conducted in 16 healthcare facilities in Japan during the Deltadominant period (August-September 2021) and the Omicron-dominant period (January-March 2022). Vaccine effectiveness (VE) against symptomatic severe acute respiratory syndrome coronavirus 2 infection was calculated for 2 doses for the Deltadominant period and 2 or 3 doses for the Omicron-dominant period compared with unvaccinated individuals.
Results. The analysis included 5795 individuals with 2595 (44.8%) cases. Among vaccinees, 2242 (55.8%) received BNT162b2 and 1624 (40.4%) received messenger RNA (mRNA)-1273 at manufacturer-recommended intervals. During the Delta-dominant period, VE was 88% (95% confidence interval [CI], 82–93) 14 days to 3 months after dose 2 and 87% (95% CI, 38–97) 3 to 6 months after dose 2. During the Omicron-dominant period, VE was 56% (95% CI, 37–70) 14 days to 3 months since dose 2, 52% (95% CI, 40–62) 3 to 6 months after dose 2, 49% (95% CI, 34–61) 6+ months after dose 2, and 74% (95% CI, 62–83) 14+ days after dose 3. Restricting to individuals at high risk of severe COVID-19 and additional adjustment for preventive measures (ie, mask wearing/high-risk behaviors) yielded similar estimates, respectively.
Conclusions. In Japan, where most are infection-naïve, and strict prevention measures are maintained regardless of vaccination status, 2-dose mRNA vaccines provided high protection against symptomatic infection during the Delta-dominant period and moderate protection during the Omicron-dominant period. Among individuals who received an mRNA booster dose, VE recovered to a high level., Clinical infectious diseases, 76(3), pp.e108-e115; 2023},
 pages = {e108--e115},
 title = {Coronavirus Disease 19 (COVID-19) Vaccine Effectiveness Against Symptomatic Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection During Delta-Dominant and Omicron-Dominant Periods in Japan: A Multicenter Prospective Case-control Study (Factors Associated with SARS-CoV-2 Infection and the Effectiveness of COVID-19 Vaccines Study)},
 volume = {76},
 year = {2023}
}