U.S. Centers for Disease Control and Prevention.Both Pfizer-BioNTech and Moderna report that their two-dose vaccines given at the appropriate intervals show approximately 94%-95% efficacy at preventing both mild and severe symptoms of COVID-19.RELATED: COVID-19 vaccines: More side effects reported after 2nd dose, but experts say there’s a reasonSo while the COVID-19 vaccines are effective at keeping people from displaying symptoms, researchers are still learning how well the shots prevent individuals from spreading SARS-COV-2, the virus that causes COVID-19, to others.In other words, someone vaccinated against COVID-19 could still be exposed to the virus, potentially becoming infected with or "carrying" SARS-COV-2 but without symptoms.