Homologous and Heterologous Prime-Boost Vaccination: Impact on Clinical Severity of SARS-CoV-2 Omicron Infection among Hospitalized COVID-19 Patients in Belgium

Abstract

We investigated effectiveness of (1) mRNA booster vaccination versus primary vaccination only and (2) heterologous (viral vector–mRNA) versus homologous (mRNA–mRNA) prime-boost vaccination against severe outcomes of BA.1, BA.2, BA.4 or BA.5 Omicron infection (confirmed by whole genome sequencing) among hospitalized COVID-19 patients using observational data from national COVID-19 registries. In addition, it was investigated whether the difference between the heterologous and homologous prime-boost vaccination was homogenous across Omicron sub-lineages. Regression standardization (parametric g-formula) was used to estimate counterfactual risks for severe COVID-19 (combination of severity indicators), intensive care unit (ICU) admission, and in-hospital mortality under exposure to different vaccination schedules. The estimated risk for severe COVID-19 and in-hospital mortality was significantly lower with an mRNA booster vaccination as compared to only a primary vaccination schedule (RR = 0.59 [0.33; 0.85] and RR = 0.47 [0.15; 0.79], respectively). No significance difference was observed in the estimated risk for severe COVID-19, ICU admission and in-hospital mortality with a heterologous compared to a homologous prime-boost vaccination schedule, and this difference was not significantly modified by the Omicron sub-lineage. Our results support evidence that mRNA booster vaccination reduced the risk of severe COVID-19 disease during the Omicron-predominant period.

Monitoring COVID‐19 vaccine effectiveness against COVID‐19 hospitalisation and death using electronic health registries in ≥65 years old population in six European countries, October 2021 to November 2022

“…Because of this, EHR has become a core data source for COVID-19 VE studies in many countries. 2,3,7,[9][10][11][12][13] By the end of 2021, the European Centre for Disease Prevention and Control (ECDC) established the Vaccine Effectiveness, Burden and Impact Studies of COVID-19 and Influenza (VEBIS) project to monitor the effectiveness of vaccines in real-world conditions and to inform public health actions and adaptation of vaccination programmes in the EU/EEA countries. One component of VEBIS is based on estimating VE using routinely collected vaccination and outcome data from EHR.…”

“…The use of population‐based Electronic‐Health Registries (EHR) has the advantage of large sample sizes and being readily available, allowing prospective timely monitoring of VE and with relatively few extra resources. Because of this, EHR has become a core data source for COVID‐19 VE studies in many countries 2,3,7,9–13 …”

“…Because of this, EHR has become a core data source for COVID‐19 VE studies in many countries. 2 , 3 , 7 , 9 , 10 , 11 , 12 , 13 …”