Clade x

Tom Inglesby, MD, director of the Center, will play the White House national security advisor.

http://www.centerforhealthsecurity.org/newsroom/center-news/2018/2018-04-16_clade-x-players-named.html

WHO declared on pandemic on 3/11

From and including: Tuesday, May 15, 2018
To, but not including Wednesday, March 11, 2020

Result: 666 days

It is 666 days from the start date to the end date, but not including the end date.

Or 1 year, 9 months, 25 days excluding the end date.

Or 21 months, 25 days excluding the end date.