Background Although several COVID-19 vaccines initially showed high efficacy, there have been concerns due to 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 Delta-dominant period (August-September 2021) and the Omicron-dominant period (January-March 2022). Vaccine effectiveness (VE) against symptomatic SARS-CoV-2 infection was calculated for 2 doses for the Delta-dominant period and 2 or 3 doses for the Omicron-dominant period, compared to 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 mRNA-1273 at manufacturer-recommended intervals. During the Delta-dominant period, VE was 88% (95% CI: 82-93) 14 days-3 months after dose 2 and 87% (95% CI: 38-97) 3-6 months after dose 2. During the Omicron-dominant period, VE was 56% (95% CI: 37-70) 14 days-3 months since dose 2, 52% (95% CI: 40-62) 3-6 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 (i.e. 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.

中文翻译：

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COVID-19 疫苗在日本 Delta 主导和 Omicron 主导时期对症状性 SARS-CoV-2 感染的有效性：一项多中心前瞻性病例对照研究（FASCINATE 研究）

背景 尽管几种 COVID-19 疫苗最初显示出高效，但由于免疫力下降和具有免疫逃逸能力的变异体的出现，人们一直担心。方法 在 Delta 主导时期（2021 年 8 月至 9 月）和 Omicron 主导时期（2022 年 1 月至 3 月），在日本的 16 家医疗机构进行了一项测试阴性设计病例对照研究。与未接种疫苗的个体相比，针对有症状的 SARS-CoV-2 感染的疫苗有效性 (VE) 计算为 Delta 优势期接种 2 剂，Omicron 优势期接种 2 剂或 3 剂。结果 分析包括 5795 人和 2595 (44.8%) 个病例。在疫苗接种者中，2242 人 (55.8%) 接受了 BNT162b2，1624 人 (40.4%) 按照制造商建议的时间间隔接受了 mRNA-1273。在 Delta 主导时期，VE 为 88%（95% CI：82-93）第 2 剂后 14 天至 3 个月，第 2 剂后 3-6 个月为 87%（95% CI：38-97）。在 Omicron 主导期间，VE 为 56%（95% CI：37- 70) 第 2 剂后 14 天至 3 个月，52% (95% CI: 40-62) 第 2 剂后 3-6 个月，49% (95% CI: 34-61) 第 2 剂后 6 + 个月，和 74 % (95% CI: 62-83) 第 3 次给药后 14 天以上。限制为重度 COVID-19 高危人群和对预防措施（即戴口罩/高危行为）的额外调整分别产生了相似的估计值. 结论 在大多数未感染过且无论疫苗接种状态如何都保持严格预防措施的日本，2 剂 mRNA 疫苗在 Delta 优势时期提供了针对症状感染的高度保护，在 Omicron 优势时期提供了中度保护。