“Currently, we do not have enough data to be able to say with confidence that the vaccines can prevent transmission,” Fauci said in a tweet during an online Q&A session. “So even if vaccinated, you may still be able to spread the virus to vulnerable people.”

What the vaccines’ clinical trials have shown, however, is that the drugs are highly effective at preventing symptomatic infections in people who have been inoculated. Both Pfizer-BioNTech’s and Moderna’s vaccines, the only two in the U.S. that have received emergency authorization so far, have proven to be roughly 95% effective at preventing symptomatic infection in people given two doses spread out weeks apart.

Johnson & Johnson’s vaccine, a one-dose jab that has yet to be granted the same authorization from the federal government, reported on Friday that its vaccine was 66% effective overall in protecting against Covid-19 in clinical trials. While lower than the others, it’s still above the threshold the federal government set — roughly 50% — to be granted emergency authorization.