<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Toon Braeye</style></author><author><style face="normal" font="default" size="100%">Lucy Catteau</style></author><author><style face="normal" font="default" size="100%">Ruben Brondeel</style></author><author><style face="normal" font="default" size="100%">Joris Van Loenhout</style></author><author><style face="normal" font="default" size="100%">Kristiaan Proesmans</style></author><author><style face="normal" font="default" size="100%">Laura Cornelissen</style></author><author><style face="normal" font="default" size="100%">Herman Van Oyen</style></author><author><style face="normal" font="default" size="100%">Veerle Stouten</style></author><author><style face="normal" font="default" size="100%">Pierre Hubin</style></author><author><style face="normal" font="default" size="100%">Matthieu Billuart</style></author><author><style face="normal" font="default" size="100%">Achille Djiena</style></author><author><style face="normal" font="default" size="100%">Romain Mahieu</style></author><author><style face="normal" font="default" size="100%">Hammami, Naïma</style></author><author><style face="normal" font="default" size="100%">Dieter Van Cauteren</style></author><author><style face="normal" font="default" size="100%">Chloé Wyndham-Thomas</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Vaccine effectiveness against onward transmission of SARS-CoV2-infection by variant of concern and time since vaccination, Belgian contact tracing, 2021.</style></title><secondary-title><style face="normal" font="default" size="100%">Vaccine</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Ad26COVS1</style></keyword><keyword><style  face="normal" font="default" size="100%">Aged</style></keyword><keyword><style  face="normal" font="default" size="100%">Aged, 80 and over</style></keyword><keyword><style  face="normal" font="default" size="100%">Bayes Theorem</style></keyword><keyword><style  face="normal" font="default" size="100%">Belgium</style></keyword><keyword><style  face="normal" font="default" size="100%">BNT162 Vaccine</style></keyword><keyword><style  face="normal" font="default" size="100%">Contact Tracing</style></keyword><keyword><style  face="normal" font="default" size="100%">COVID-19</style></keyword><keyword><style  face="normal" font="default" size="100%">Humans</style></keyword><keyword><style  face="normal" font="default" size="100%">middle aged</style></keyword><keyword><style  face="normal" font="default" size="100%">RNA, Viral</style></keyword><keyword><style  face="normal" font="default" size="100%">SARS-CoV-2</style></keyword><keyword><style  face="normal" font="default" size="100%">Vaccination</style></keyword><keyword><style  face="normal" font="default" size="100%">Vaccine Efficacy</style></keyword><keyword><style  face="normal" font="default" size="100%">vaccines</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2022</style></year><pub-dates><date><style  face="normal" font="default" size="100%">2022 May 11</style></date></pub-dates></dates><volume><style face="normal" font="default" size="100%">40</style></volume><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;p&gt;&lt;b&gt;BACKGROUND: &lt;/b&gt;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.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;METHODS: &lt;/b&gt;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.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;FINDINGS: &lt;/b&gt;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&amp;nbsp;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&amp;nbsp;days after vaccination). We observed lower initial VEi in the age group 65-84&amp;nbsp;years (32% vs 46% in the age group 45-64&amp;nbsp;years for BNT162b2) and faster waning. Hybrid immunity waned slower than vaccine-induced immunity.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;INTERPRETATION: &lt;/b&gt;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.&lt;/p&gt;
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