One out of three parents in the U.S. do not plan to have their children vaccinated against the flu—even though public health experts agree that getting the shot is more important than ever this year. The C.S. Mott Children’s Hospital National Poll on Children’s Health found the most common reasons for not having a child immunized are concerns about side effects or a belief that it is not necessary or effective. About a third of parents reported that their medical provider doesn’t strongly suggest the flu shot. While the effectiveness of the shot does vary from year to year—it was 45 percent effective last year—health officials say it’s the best way to avoid the virus that killed between 24,000 and 62,000 people last season.