Ensuring COVID-19 Vaccines Work

Before the U.S. Food and Drug Administration (FDA) determines whether to approve a vaccine or authorize a vaccine for emergency use, clinical trials are conducted to determine how well it works. This is known as effectiveness.After FDA approves a vaccine or authorizes a vaccine for emergency use, it continues to be studied to determine how well it works under real-world conditions. CDC and other federal partners will be assessing COVID-19 vaccine effectiveness under real-world conditions. CDC is preparing now so that further assessment of vaccine effectiveness can start as soon as COVID-19 vaccines either approved or authorized for emergency use by FDA. Many of these assessments will build on existing CDC programs