<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>13</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Marjan Meurisse</style></author><author><style face="normal" font="default" size="100%">Nina Van Goethem</style></author><author><style face="normal" font="default" size="100%">Joris Van Loenhout</style></author><author><style face="normal" font="default" size="100%">Toon Braeye</style></author><author><style face="normal" font="default" size="100%">Lucy Catteau</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Homologous versus heterologous prime-boost COVID-19 vaccination: impact on clinical severity of Omicron among hospitalized COVID-19 patients in Belgium</style></title><secondary-title><style face="normal" font="default" size="100%">European Society of Clinical Microbiology and Infectious Diseases</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">2023</style></year><pub-dates><date><style  face="normal" font="default" size="100%">17/04/2023</style></date></pub-dates></dates><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;p&gt;&lt;strong&gt;Background&lt;/strong&gt;&lt;br&gt;
We investigated the real-world effectiveness of a heterologous versus homologous primeboost&lt;br&gt;
vaccination scheme against severe clinical outcomes of SARS-CoV-2 Omicron&lt;br&gt;
infection among hospitalized patients in Belgium, and if this effect is homogenous across&lt;br&gt;
different Omicron sub-lineages.&lt;br&gt;
&lt;strong&gt;Methods&lt;/strong&gt;&lt;br&gt;
Observational data from existing national surveillance systems and administrative sources&lt;br&gt;
were leveraged to estimate a causal effect. A Directed Acyclic Graph was formalized to&lt;br&gt;
identify confounding factors. The target population consisted of adult COVID-19 patients&lt;br&gt;
admitted to a Belgian hospital after the start of the booster vaccination campaign. Only&lt;br&gt;
patients with a SARS-CoV-2 Omicron infection (BA.1, BA.2, or BA.4 and BA.5 combined&lt;br&gt;
(BA.4/5) sub-lineages) confirmed by whole genome sequencing and vaccinated with a&lt;br&gt;
homologous (mRNA for prime/mRNA for boost) or heterologous (viral vector for&lt;br&gt;
prime/mRNA for boost) prime-boost vaccination schedule were included in the study&lt;br&gt;
population. An adjusted logistic model was build and g-computation was executed to&lt;br&gt;
estimate counterfactual risks of different clinical severity outcomes (intensive care unit (ICU)&lt;br&gt;
transfer, in-hospital mortality, and severe COVID-19 – defined as experiencing an acute&lt;br&gt;
respiratory distress syndrome (ARDS) event, or an ICU transfer, or in-hospital mortality) for&lt;br&gt;
patients that received a homologous versus heterologous prime-boost vaccination, and to&lt;br&gt;
contrast those. The role of the Omicron sub-lineage as an effect modifier was investigated by&lt;br&gt;
estimating and contrasting these counterfactual risks across different sub-lineages.&lt;br&gt;
&lt;strong&gt;Results&lt;/strong&gt;&lt;br&gt;
756 patients (499 homologous, 257 heterologous prime-boost vaccination) were included in&lt;br&gt;
the study population. No significant difference in counterfactual risks for severe COVID-19&lt;br&gt;
(RD=-0.04, 95%CI [-0.10–0.02]), ICU transfer (RD=-0.03, 95%CI [-0.07–0.02]), or inhospital&lt;br&gt;
mortality (RD=0.00, 95%CI [-0.05–0.04]) was found between homologous versus&lt;br&gt;
heterologous prime-boost vaccination, and no significant effect modification of the Omicron&lt;br&gt;
sub-lineage could be observed.&lt;br&gt;
&lt;strong&gt;Conclusions&lt;/strong&gt;&lt;br&gt;
Our results suggest that there is no difference in protection against severe disease among&lt;br&gt;
hospitalized COVID-19 patients offered by the contrasted prime-boost vaccination schemes.&lt;br&gt;
These results can inform vaccine policy, and contribute to knowledge used for the&lt;br&gt;
development of strategies for booster campaigns during the continuous COVID-19 crisis.&lt;/p&gt;
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