31 March 2021 This article is part of a series of explainers on vaccine development and distribution. Learn more about vaccines – from how they work and how they’re made to ensuring safety and equitable access – in WHO’s Vaccines Explained series. Countries around the world are rolling out COVID-19 vaccines, and a key topic of interest is their safety. Vaccine safety is one of WHO’s highest priorities, and we’re working closely with national authorities to develop and implement standards to ensure that COVID-19 vaccines are safe and effective.