Dr. John Brownstein, ABC News medical contributor, breaks down COVID-19 vaccinations and explains what the "double mutant variant" is and why it worries health experts. SUBSCRIBE to ABC NEWS: https://bit.ly/2vZb6yP Watch More on http://abcnews.go.com/ LIKE ABC News on FACEBOOK https://www.facebook.com/abcnews FOLLOW ABC News on TWITTER: https://twitter.com/abc