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Vaccine Effectiveness Against COVID19-Infection and Onward Transmission by Variant of Concern and Time Since Vaccination, Belgian Contact Tracing, 2021
28 Pages Posted: 4 Jan 2022
More...Abstract
Background: During the first half of 2021, we observed high vaccine effectiveness (VE) against SARS-CoV2-infection. The replacement of the alpha-‘variant of concern’ (VOC) by the delta-VOC and uncertainty about the time course of immunity called-for a re-assessment.
Methods: We estimated VE against transmission of infection (VET) from Belgian contact tracing data for high-risk contacts between 26/01/2021 and 30/11/2021 by two components: susceptibility of the contact (VEs) and infectiousness of breakthrough cases (VEi) for a complete schedule of Ad26.COV2.S, ChAdOx1, BNT162b2, mRNA-1273 as well as infection-acquired and hybrid immunity. We adjusted for personal characteristics (age, sex, household), background exposure and duration of exposure.
Findings: VET-estimates were higher for mRNA-vaccines, over 90%, compared to viral vector vaccines: 63% and 78% for Ad26COV2.S and ChAdOx1 respectively (alpha-VOC, 0-50 days after vaccination). Waning rates were comparable across vaccine brands, with a 50% VEs-reduction in 198 (95%CI 181-224) days and a 50% VEi-reduction in 175 (95%CI 145-248) days. We observed faster waning of VEi in the age group 65-84 years. The delta-VOC was associated with a 40% increase in odds of transmission and a decrease of VEs (69 to 56%) and especially of VEi (73 to 45% for BNT162b2). Infection-acquired and hybrid immunity were less affected by the delta-VOC and waned slower than vaccine-induced immunity.
Interpretation: VET-estimates, while remaining significant, were reduced by the delta-VOC and waned over time. We observed faster waning in males and the age group 65-84 years. We should seek to improve vaccine-induced protection in these persons, especially when vaccinated with viral-vector vaccines.
Funding Information: This study was supported by the Belgian Federal and Regional Authorities through funding for the LINK-VACC project and organizing and financing of contact tracing.
Declaration of Interests: No conflicts of interest.
Ethics Approval Statement: Data linkage and collection within the data-warehouse has been approved by the information security committee.
Keywords: vaccine effectiveness, Transmission, SARS-CoV2, infection, contact tracing, susceptibility, infectiousness, Bayesian analysis, Covid19
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