Effectiveness of mRNA COVID-19 vaccines against symptomatic SARS-CoV-2 infections during the SARS-CoV-2 Omicron BA.1 and BA.2 epidemic in Japan: vaccine effectiveness real-time surveillance for SARS-CoV-2 (VERSUS)

• Main Authors: Haruka Maeda (Author), Nobuo Saito (Author), Ataru Igarashi (Author), Masayuki Ishida (Author), Mayumi Terada (Author), Takayasu Ito (Author), Hideko Ikeda (Author), Hiroshi Kamura (Author), Iori Motohashi (Author), Yuya Kimura (Author), Masaru Komino (Author), Hiromi Arai (Author), Osamu Kuwamitsu (Author), Nobuhiro Akuzawa (Author), Eiichiro Sando (Author), Toru Morikawa (Author), Haruki Imura (Author), Hiroki Inoue (Author), Tomoichiro Hayakawa (Author), Osamu Teshigahara (Author), Yasuji Ohara (Author), Motoi Suzuki (Author), Konosuke Morimoto (Author)
• Format: Book
• Published: Taylor & Francis Group, 2023-12-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.
• Notes: 1476-0584; 1744-8395; 10.1080/14760584.2023.2188950
• Keywords: ba.1; ba.2; covid19; japan; omicron; sarscov2; vaccine effectiveness; Internal medicine; RC31-1245
• Source: Expert Review of Vaccines, Vol 22, Iss 1, Pp 288-298 (2023)

Background Evaluating COVID-19 vaccine effectiveness (VE) domestically is crucial for assessing and determining national vaccination policy. This study aimed to evaluate VE of mRNA COVID-19 vaccines in Japan. Methods We conducted a multicenter test-negative case-control study. The study comprised individuals aged ≥16 visiting medical facilities with COVID-19-related signs or symptoms from 1 January to 26 June 2022, when Omicron BA.1 and BA.2 were dominant nationwide. We evaluated VE of primary and booster vaccination against symptomatic SARS-CoV-2 infections and relative VE of booster compared with primary. Results We enrolled 7,931 episodes, including 3,055 test positive. The median age was 39, 48.0% were male, and 20.5% had underlying medical conditions. In individuals aged 16 to 64, VE of primary vaccination within 90 days was 35.6% (95% CI, 19.0-48.8%). After booster, VE increased to 68.7% (60.6-75.1%). In individuals aged ≥65, VE of primary and booster was 31.2% (−44.0-67.1%) and 76.5% (46.7-89.7%), respectively. Relative VE of booster compared with primary vaccination was 52.9% (41.0-62.5%) in individuals aged 16 to 64 and 65.9% (35.7-81.9%) in individuals aged ≥65. Conclusions During BA.1 and BA.2 epidemic in Japan, mRNA COVID-19 primary vaccination provided modest protection. Booster vaccination was necessary to protect against symptomatic infections.