A new population-based study has applied the BRAVE (Benefit-Risk Assessment of Vaccines) toolkit to evaluate Vaxzevria, the AstraZeneca COVID-19 vaccine, across the European Union. Developed in collaboration with the EMA, BRAVE is designed to deliver real-time, data-driven assessments of vaccines’ public health impact, supporting evidence-based decisions in emergency and routine contexts.
How the BRAVE Toolkit Works
BRAVE is more than a model—it’s a modular toolkit combining epidemiological data, statistical code, and an interactive dashboard. It allows users to simulate and compare vaccine benefits and risks in specific populations.
- Input data includes age-stratified COVID-19 cases, hospitalisations, ICU admissions, deaths, and vaccination coverage, sourced from EU-wide databases such as TESSy, ECDC, and EudraVigilance.
- Adverse event risk, like TTS, was calculated by comparing observed post-vaccine cases to background incidence rates (which, for TTS, were considered zero given its novelty).
- Vaccine effectiveness was drawn from real-world studies and applied conservatively, accounting for age, variant prevalence, and time since vaccination.
- Missing data (e.g., age or sex) were handled using imputation methods, ensuring robustness.
- The model does not include indirect (herd) immunity, but does allow for waning effectiveness over time.
The BRAVE dashboard enables scenario testing, e.g., changing variant prevalence or adjusting for multiple imputation methods. It was built with transparency in mind, incorporating input from healthcare professionals and communication experts to ensure usability across European regulatory bodies.
Key Findings
The study covers December 2020 to December 2021 and includes over 69 million administered doses across 30 EU/EEA countries. By integrating real-world data, such as infection rates, hospitalisation numbers, and vaccine coverage, the BRAVE model quantified Vaxzevria’s population-level impact.
Preventive Impact
According to BRAVE estimates, Vaxzevria prevented:
- 855,105 symptomatic COVID-19 cases
- 87,243 hospital admissions
- 18,493 ICU admissions
- 14,234 deaths across the EU/EEA
Risk Considerations
These significant benefits were weighed against the known risk of thrombosis with thrombocytopenia syndrome (TTS), which remained low (1.6 cases per 100,000 first doses). The resulting benefit–risk balance was favourable across all age groups, particularly for those aged 60–69.
A Flexible Tool for Public Health Decisions
BRAVE stands out for its adaptability. It integrates evolving data, like new variants or vaccine types, and assesses outcomes across demographics and time. It supports regulators and national immunisation bodies with a dynamic framework for pharmacovigilance and policy.
Limitations and Future Directions
Limitations include reliance on spontaneous adverse event reporting, absence of individual-level dosing data, and lack of natural immunity modelling. Although the toolkit doesn’t yet include uncertainty modelling, future updates may incorporate Monte Carlo simulations.
Expanding BRAVE to include booster doses, sex-specific data, or other vaccines needs further development and detailed data. Standardized data collection across countries is essential for enhancing digital health tools and pandemic preparedness.
For more details, access the full study here: The Lancet Digital Health.
