Can You Still Spread Covid-19 After You Get Vaccinated?

Do the Covid vaccines prevent you from spreading the virus, or do they just protect you from getting sick?

Scientists don’t know yet—and the uncertainty has big implications during the rollout of the vaccines.

Pfizer and Moderna, the companies that developed the vaccines authorized in the U.S. so far, say their vaccines are about 95% effective at preventing people from getting sick with Covid symptoms. But there’s not enough evidence yet on whether the vaccines also prevent asymptomatic infection and transmission.

The companies say research is ongoing to determine the answer. Without vaccines, research has suggested that asymptomatic transmission of the coronavirus that causes Covid is responsible for roughly a quarter of infections.

The result, experts say, is that precautions like wearing masks, social distancing and avoiding crowded spaces will be necessary until the country gets closer to herd immunity, the point at which enough people are immune to a disease to make its spread unlikely. Some studies have estimated roughly 75% to 80% of the U.S. population needs to be immune to Covid-19 to reach herd immunity, but that number is a moving target and could rise as new variants emerge.