The first indication of how well the flu vaccine is working this season in America just came out — and it may help explain why this year’s flu season is milder than last year’s. According to the new report, people who’ve gotten the shot this season reduced their risk of needing medical care for serious flu complications by about half. For context, last year’s flu shot cut people’s risk of infection from the most commonly circulating influenza strain by only a quarter. It was also one of the worst flu seasons in recent memory, when influenza-associated deaths reached 80,000. The Centers for Disease Control and Prevention measure the vaccine’s effectiveness by looking at how many people are showing up in doctors’ offices and hospitals with flu, as well as tallying up flu-related hospitalization and death numbers.