The rapid rollout of COVID-19 vaccines was essential, but questions and concerns arose about rare side effects, such as thrombosis with thrombocytopenia syndrome (TTS) linked to the Vaxzevria (AstraZeneca) vaccine. Assessing whether the benefits of vaccination still outweigh these potential risks is complex. In our latest work published in The Lancet Digital Health, we introduce the Benefit Risk Assessment of Vaccines (BRAVE) toolkit, designed to provide a clearer, data-driven picture to support public health decisions.
Making sense of vaccine safety requires looking beyond just the number of adverse events. The BRAVE toolkit uses a probabilistic model that integrates data from multiple large-scale EU sources, including disease surveillance (TESSy), adverse event reporting (EudraVigilance), vaccination records (ECDC), and demographics (EUROSTAT). The model estimates the vaccine's benefits, such as preventing COVID-19 cases, hospitalisations, ICU admissions, and deaths by comparing real-world observations to what would likely have happened without the vaccine. It simultaneously calculates the observed risks associated with vaccination. Results are presented via an interactive web application, allowing for exploration by different age groups.
The Vaxzevria case: a BRAVE perspective on vaccine safety
We applied the BRAVE toolkit to the Vaxzevria vaccine in the EU up to the end of 2021. Our analysis found that, despite the confirmed rare risk of TTS (most frequent in women aged 30-59 and men aged 20-29), the vaccine offered significant protection. Based on the data, Vaxzevria vaccination was estimated to prevent, per 100,000 people vaccinated:
- 12,113 COVID-19 cases
- 1140 hospitalisations
- 184 ICU admissions
- 261 deaths
The benefits clearly outweighed the risks of TTS across all age groups, with the oldest age groups seeing the largest reduction in severe outcomes like hospitalisations and death.
Context is key
The real added value of the BRAVE toolkit is its ability to contextualize vaccine risks relative to benefits using comprehensive, real-world data–something previous tools didn't specifically address for COVID-19 vaccines. This provides crucial evidence to support regulatory decisions and national vaccination strategies. However, the power of such tools relies heavily on access to high-quality, granular, and timely real-world data, underscoring the need for improved data collection and standardization across countries.
Furthermore, the value of tools like BRAVE is maximized through ongoing updates, integrating new data on virus variants or vaccine performance as it emerges to ensure assessments remain relevant. The methodology presented here isn't limited to Vaxzevria or TTS because the adaptable framework can be applied to other vaccines or health threats. However, tailoring it precisely may require adjustments for different pathogen characteristics. This adaptability strengthens preparedness for future public health emergencies by allowing rapid, evidence-based assessments.
It has been great to work together with our collaborators at the European Medicines Agency and University of Dundee. Congrats to all the authors!
