Bivalent mRNA vaccine effectiveness against COVID-19 among older adults in Japan: a test-negative study from the VENUS study

Table 2 Absolute or relative VE of bivalent vaccines against infection

	Absolute VE^ab, % (95% CI)	Absolute VE^ac, % (95% CI)	Relative VE^a, % (95% CI)	Relative VE^a, % (95% CI)
Vaccination status
Unvaccinated	Ref	Ref	—	—
≥ 2 monovalent doses	18.8 (4.9, 30.7)	—	Ref	—
2 monovalent doses	—	12.8 (-11.4, 31.7)	—	Ref
3 monovalent doses	—	23.2 (7.1, 36.4)	—	11.9 (-10.0, 29.4)
4 monovalent doses	—	18.3 (4.1, 30.4)	—	6.4 (-14.1, 23.2)
≥ 2 monovalent doses plus a bivalent dose	33.6 (20.8, 44.3)	33.5 (20.7, 44.3)	18.2 (9.4, 26.0)	23.8 (6.0, 38.2)

Analyzed test results were from 17,080 participants (age: 80.9 ± 7.7 years [mean ± standard deviation], 42.3% male). Logistic regression analyses with cluster robust standard errors at the individual level were conducted to estimate the ORs and 95% CIs for testing positive according to the vaccination status. VE was defined as (1 − OR) × 100%
Abbreviations: VE vaccine effectiveness, CI confidence interval, OR odds ratio
^aAdjusted for sex, age group, number of comorbidities, infection history, residential municipality, and test week
^bThis analysis was conducted to assess the effectiveness of receiving ≥ 2 doses of monovalent vaccines compared with unvaccinated status since receiving ≥ 2 doses of monovalent vaccines were required to receive a dose of bivalent vaccines
^cThis analysis was conducted to assess the differences in the effectiveness of completing only primary series (2 monovalent doses), receiving one booster dose (3 monovalent doses), and receiving two booster doses (4 monovalent doses) compared with unvaccinated status since a variety of vaccinated status were assumed during the study period

ISSN: 1471-2334