New study: Counties with mask mandates had significantly LOWER #covid19 cases (starting a few weeks after the mandate was implemented, consistent with #covid19 transmission dynamics).

Takeaway: once again, during surges, masks matter.https://t.co/bQWb4vUD1j pic.twitter.com/rTTdEZfoFc

— Megan Ranney MD MPH 🌻 (@meganranney) February 21, 2022