Researchers at the University of Oxford say they’ve discovered a huge breakthrough related to the vaccine they developed with AstraZeneca—it dramatically slows down transmission of the coronavirus. That means the Oxford/AstraZeneca shot is the first coronavirus vaccine that has been shown to hinder the virus’ ability to spread from person to person, rather than just protect people from becoming infected by it. Matt Hancock, the British health secretary, celebrated the results as “absolutely superb,” and told BBC News that it now seems likely “this jab works not only to keep you safe but to keep you from passing on the virus to others.” The United States has agreed to buy 300 million doses of the AstraZeneca vaccine, but it’s yet to follow Britain in approving the shot for a mass rollout.