I don't understand the use of "know" here. Who know? Does "to the American people — know there is nothing to worry about" mean "to the American people — (you should) know there is nothing to worry about"?
The problem is that I feel "you should" has a tone of more commanding than persuading. Perhaps with only "know" there the tone would be euphemized. I am not sure.
What does "know" mean there?
Biden tweeted 2h ago:
Today, I received the COVID-19 vaccine.
To the scientists and researchers who worked tirelessly to make this possible — thank you. We owe you an awful lot.
And to the American people — know there is nothing to worry about. When the vaccine is available, I urge you to take it.