On April 7, 2021, the European Medical Agency (EMA) concluded that thrombosis in combination with thrombocytopenia has been identified as a likely adverse event following vaccination with the COVID-19 vaccine Vaxzevria. Researchers from the Mathematical Modelling of Infectious Diseases Unit at the Institut Pasteur used a mathematical model to assess its benefits and risks in metropolitan France accounting for the indirect effect of vaccination as well as the availability of alternative vaccines. Across a range of scenarios, the benefits associated with Vaxzevria distribution in people 55 years and older largely outperformed the risks of death from COVID-19. In young adults, the risks were higher than or of similar magnitude as the benefits. These results contributed to the National Autority of Health (HAS) and ANSM (French agency for medicine and health products) recommendations.