Bruce G. Gellin

It's very, very difficult for us to study with faith and trust that we're getting the results that we need, he said.

Dr. Bruce Gellin, a former federal vaccine safety official, said the external researchers were tapped long ago to establish trust with people who doubted government assurances about vaccines.

He said Mr. Kennedy's concerns appeared to reflect his biases in favor of studies finding that vaccines cause harm.

I think basically the premise is if you don't find what I believe, he said, I'm going to believe what you find.