There are still a lot of questions about the vaccines, like how long they're effective.
If you get the Moderna vaccine, you're safe from the coronavirus for one year.
The company says it's confident it that two doses of the vaccine provides immunity for that period of time.
Moderna is on track to deliver at least 600 million – and up to one billion doses – of its vaccine by the end of this year.
The U.S. has bought 200-million doses.
The Moderna vaccine is also being rolled out in several other countries.
The U.K. approved the vaccine just last week.