Senior Clinical Epidemiologist European Medicines Agency Amsterdam, Netherlands
Background: During the COVID-19 pandemic, there was a need to rapidly assess complex data from various sources to assess the benefit and risk of COVID-19 vaccines and its impact on public health.
Objectives: This work aims to generate a digital tool to support policy makers in the benefit and risk contextualisation of COVID-19 vaccines in the EU while relying on a minimum set of publicly available data, using thrombosis with thrombocytopenia syndrome (TTS) related to the adenovirus vaccine, Vaxzevria, as a use case.
Methods: The toolkit was developed using various aggregated data sources containing information on COVID-19 incidence and vaccine coverage from Member States of the EU/EEA (ECDC), variants of concern (TESSy), spontaneous reports (EudraVigilance), background incidence (EMA) and published literature. Prevented burden was calculated, using a probabilistic model, by comparing the observed number of confirmed COVID-19 cases, hospitalisations, ICU admissions and deaths with the expected number of these events among the EU population, had no COVID-19 vaccines been available, between January 2020 and March 2021. The analysis was performed stratified by age groups using the available data at the time when the toolkit was developed (dd. February 2022). The risk of TTS associated with Vaxzevria was assessed by comparing the observed risk events to the expected events based on background incidence rates. The toolkit allows to perform simultaneous analysis with different scenarios and different parameters for vaccine effectiveness, variants of concern, vaccine coverage, weighting background risk estimates. Moreover, it allows for imputation of missing data and redistribution of age categories.
Results: The toolkit generates stratified charts and tables which showed the benefits and risks of Vaxzevria vaccination across age groups. The probabilistic model estimated the benefit of Vaxzevria vaccination by the prevention per 100,000 vaccines of 12,113 confirmed COVID-19 infections, 1,140 COVID-19 hospitalisations, 184 ICU admissions and 261 COVID-19 related deaths in the EEA, between January 2020 and March 2021. Both the prevented burden, as well as the expected additional cases of TTS after Vaxzevria vaccination were the highest in the 60 to 69 years of age category, with benefits outweighing the risk in all age groups.
Conclusions: The digital tool proved that the benefits of Vaxzevria outweigh the TTS risk. The proposed methodology has the potential to be applied to other serious adverse events associated with COVID-19 or other vaccines. Further work will be conducted to validate the tool using other outcomes and settings to strengthen preparedness and to support policy makers in the design of vaccination campaigns.
