A vaccine is only approved if its quality, efficacy and safety have been sufficiently demonstrated. That is why the clinical studies are so important. In the final phase, COVID-19 vaccines are tested on large groups of people, often tens of thousands of people. In the case of the COVID-19 vaccines, this is between 20,000 and 60,000 people. Thanks to these studies, we can see if and what side-effects may occur. Most side-effects become visible within 6 weeks after vaccination. These are discovered during the clinical studies. So the risk of serious side effects after vaccination with one of the approved COVID-19 vaccines is very small. After approval, COVID-19 vaccines are closely monitored by the European Medicines Agency (EMA) and others in order to investigate the very rare side effects (if they occur).