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)

ABSTRACT

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.

KEYWORDS:

• BA.1
• BA.2
• COVID19
• Japan
• omicron
• SARSCoV2
• vaccine effectiveness

Supplemental data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/14760584.2023.2188950.

Acknowledgments

We are grateful to medical staff of the participating hospitals and clinics. We thank Rina Kubo, Yumi Araki, Kyoko Uchibori, Rina Shiramizu, Fumiyo Tsujita (Institute of Tropical Medicine, Nagasaki University), and Daichi Hatahara (Nagasaki University) for their assistance

Declaration of interest

H Maeda reports lecture and consulting fees from Moderna Inc and participating in Pfizer Inc-funded research outside this work. A Igarashi reports grants from Takeda Pharmaceutical Inc, consulting fees from Pfizer Inc and Astra Zeneca Inc, and lecture fees from Takeda Pharmaceutical Inc, Shionogi Inc, Janssen Pharma Inc, and Modera Inc outside this work. M Terada reports lecture fees from Astra Zeneca outside this work. T Ito reports stock ownership of Takeda Pharmaceutical Inc. H Imura reports participating in research funded by Pfizer Inc, research funded by GENOVA Inc, research funded by Astra Zeneca Inc, and research funded by FUJIFILM Toyama Chemical CO., Ltd. outside this work. T Hayakawa reports stock ownership of Takeda Pharmaceutical Inc. and Daiichi Sankyo Healthcare Co., Ltd. K Morimoto reports grants from Pfizer Inc, consulting fees from Moderna Inc, and lecture fees from MSD outside this work. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or material discussed in the manuscript apart from those disclosed.

Author contributions

HM, NS, AI, MI, MT, MS, and KM conceived and designed the study. MI, MT, TI, HI, HK, IM, YK, MK, HA, OK, NA, ES, TM, HI, HI, TH, OT, and YO collected and verified the data. HM and NS did the analysis and MS supervised the analysis. AI performed the analysis separately from HM and NS. HM, NS, AI, MI, MT, MS, and KM had full access to the data. HM and KM wrote the first draft of the manuscript, and all authors provided critical review and revision of the text and approved the final version for publication.

Reviewer disclosures

Peer reviewers on this manuscript have received an honorarium for their review work. Peer reviewers on this manuscript have no other relevant financial or other relationships to disclose.

Additional information

Funding

This manuscript was funded by the Japan Agency for Medical Research and Development (Grant number: JP21fk0108612), and by the Ministry of Health, Labour and Welfare.