Billions of doses of vaccines have been given to Americans in the 30 years of the injury program’s existence. During that time, about 21,000 people filed claims . Of 18,000 claims that have been evaluated so far, roughly two-thirds have been dismissed because the program determined that the evidence showed vaccines were not at fault.

About 6,600 claims have been compensated. Most of those — about 70 percent — were settlements in cases where the program did not find sufficient evidence that vaccines caused any injury. Program officials say they usually compensate people if their medical condition and timing of symptoms match descriptions on an official list , even if there isn’t enough evidence that the vaccine was responsible.

Many claims in recent years concern the flu vaccine, which health officials now recommend annually for adults and children — and which accounts for almost half of all the vaccine doses distributed these days. Over roughly the last dozen years (from 2006 through 2017, the period for which the injury compensation program has dosage data), more than 1.5 billion doses of flu vaccine were given out. During that time, fewer than 3,500 injury claims were filed — roughly two claims for every million doses. Many of those claims do not relate to the vaccine itself, but to shoulder injuries, usually in adults, that occurred because a health provider injected a vaccine in the wrong spot on the shoulder. Public health officials say they are increasing training for health providers to help them avoid that type of mistake.