This video is unavailable because we were unable to load a message from our sponsors. If you are using ad-blocking software, please disable it and reload the page. Embed Code Restart Playing WATCH MORE VIDEOS FROM THIS EPISODE > Vaccines have reduced or eliminated many infectious diseases that have harmed or killed millions of people. Pfizer's Chief Medical Officer Dr. Freda Lewis-Hall joins E.R. physician Dr. Travis Stork to talk about the ways that vaccines work. ShareTweet