The time derivative of the logistic sigmoid is this bell-shaped curve that Obama tweeted. It's all about flattening this curve as he links to

>If you’re wondering whether it’s an overreaction to cancel large gatherings and public events (and I love basketball), here’s a useful primer as to why these measures can slow the spread of the virus and save lives. We have to look out for each other. Barack Obama (@BarackObama) March 12, 2020