What’s causing the delay in COVID vaccine distribution?

Earlier this month, the Trump administration said it expected to have enough coronavirus vaccine doses for 20 million Americans by the end of the year. But this week the Centers for Disease Control and Prevention indicated that as of Dec. 28, only 2.1 million Americans had received the first of two doses, out of approximately 11.5 million that have been distributed. It’s the end of the year, and the doses have not reached 20 million. What’s causing the lag? Yahoo News medical contributor Dr. Kavita Patel explains.