Individual businesses and local governments can still set their own rules for whether masks are required.
Several states, including Alabama and Mississippi, have lifted mandates asking people to wear masks in public.
For COVID-19, predictions of what it will take to reach herd immunity vary wildly, and it's more complicated than one magic number.
Behavioral economics helps explains why we're prone to letting our guard down.
To encourage a certain behavior, policymakers can choose carrots or sticks. There's evidence that the sticks are more effective.