It's now 100 days since the first COVID shot was given in the largest mass vaccination campaign in U.S. history. With more than 2 million shots administered daily, more vaccines are going in arms each day in America than in all of the clinical trials combined. Each vaccine's clinical trial had 30,000-40,000 participants and was required to produce data for at "least two months after completion of the full vaccination regimen to help provide adequate information to assess a vaccine's benefit-risk profile." Today, that means we are getting more and more real-world data from a larger and more diverse group than any clinical trial could ever hope to produce. And as vaccine makers continue to seek FDA authorization, the real-world data also require intense scrutiny. According to the CDC, the current vaccine safety monitoring program is one of the most intense ever. But how does it work — and is it intense enough? Aaron Kesselheim, MD, JD, MPH, professor of medicine at Harvard Medical School and Brigham and Women's Hospital in Boston, joins us on this week's episode to answer that question and explain the possible shortfalls, as well as what you should know if you need to report something.