Does the Claim that Only 1 in a Million are Harmed by Vaccines Have Any Merit?It is commonly believed that vaccines are safe. Many doctors and public health officials will tell you that serious adverse effects from vaccines are “extremely rare”—that they occur in less than “one in a million” vaccine doses given. One in a million. It sounds like pretty good odds that you would be fine. However, is this one in a million merely an idiom being used to convey the idea that the odds are very small, or is it truly a fact based on accurate and observable data?