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 exposure contacts between 26/01/2021 and 14/12/2021 by susceptibility (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 used a multilevel Bayesian model and adjusted for personal characteristics (age, sex, household), background exposure, calendar week, VOC and time since immunity conferring-event.
Findings: VET-estimates were higher for mRNA-vaccines, over 90%, compared to viral vector vaccines: 66% and 80% for Ad26COV2.S and ChAdOx1 respectively (Alpha, 0-50 days after vaccination). Delta was associated with a 40% increase in odds of transmission and a decrease of VEs (72-64%) and especially of VEi (71-46% for BNT162b2). Infection-acquired and hybrid immunity were less affected by Delta. Waning further reduced VET-estimates: from 81% to 63% for BNT162b2 (Delta, 150-200 days after vaccination). We observed lower initial VEi in the age group 65-84 years (32% vs 46% in the age group 45-64 years for BNT162b2) and faster waning. Hybrid immunity waned slower than vaccine-induced immunity.
Interpretation: VEi and VEs-estimates, while remaining significant, were reduced by Delta and waned over time. We observed faster waning in the oldest age group. We should seek to improve vaccine-induced protection in older persons and those vaccinated with viral-vector vaccines.
Keywords: Bayesian analysis; Contact Tracing; Covid19; Infection; Infectiousness; SARS-CoV2; Susceptibility; Transmission; Vaccine effectiveness.
【저자키워드】 SARS-CoV2, COVID19, susceptibility, Infection, Contact tracing, Transmission, infectiousness, vaccine effectiveness, Bayesian analysis, 【초록키워드】 Viral vector, Vaccine, vaccination, Bayesian, Immunity, Vaccines, VoC, mRNA-1273, variant, Delta, Sex, Contact tracing, BNT162b2, Ad26.COV2.S, Characteristics, household, infectiousness, mRNA, Effectiveness, Alpha, age, ChAdOx1, hybrid, Bayesian analysis, Contact, Viral vector vaccines, Vaccine-induced immunity, Older, Ad26, replacement, Complete, mRNA-vaccines, decrease, initial, IMPROVE, Course, affected, reduced, adjusted, less, faster, increase in, waned, 【제목키워드】 vaccination, variant, Effectiveness, onward transmission,