Do the Covid vaccines prevent you from spreading the virus, or do they just protect you from getting sick?
Scientists still don’t know – and the uncertainty will have a big impact when the vaccines are released.
Pfizer and Moderna, the companies that have developed the vaccines authorized so far in the U.S., say their vaccines are about 95% effective in preventing people from becoming ill with Covid symptoms. But there is not yet enough evidence that the vaccines also prevent asymptomatic infection and transmission.
The companies say research is underway to determine the answer. Without vaccines, research has suggested that asymptomatic spread of the coronavirus causes Covid for about a quarter of infections.
The result, experts say, is measures such as wearing masks, social distance and avoiding crowded places to get the country closer to herd protection, the point at which enough people immune from disease to make its spread unlikely. Some studies have estimated that approximately 75% to 80% of the U.S. population must be resistant to Covid-19 in order to achieve herd immunity, but that number is a moving target and could rise as new changes will appear.