1 dose of Moderna, Pfizer vaccines effective against COVID-19. 'Get the second dose,' experts say.

For months, data on the effectiveness of COVID-19 vaccines has been based on information from clinical trials. Now there is new, real-world data out about the effectiveness of the Pfizer-BioNTech and Moderna vaccines — and it’s very promising.

New research from the Centers for Disease Control and Prevention released on Monday found that both Pfizer’s and Moderna’s mRNA COVID-19 vaccines are exceedingly effective at preventing the disease after just one dose, at rates higher than what was previously reported.

The study analyzed data from 3,950 health care personnel, first responders and other essential and frontline workers who underwent weekly testing for SARS-CoV-2, the virus that causes COVID-19, for 13 weeks after they were vaccinated. The researchers discovered that the vaccines were 80 percent effective at preventing COVID-19 after one dose, and 90 percent effective after two doses.