Over four days and nearly 20 hours of testimony, under harsh questioning from Democrats, Health Secretary Robert F. Kennedy Jr. has repeatedly backed away from his longstanding criticism of the measles, mumps and rubella vaccine. On Wednesday, he made his strongest statement yet — albeit on behalf of his department and not himself.

“We promote the M.M.R.,” Mr. Kennedy told the Senate Finance Committee on Wednesday morning, referring to the combined vaccine for measles, mumps and rubella. “We have advised every child to get the M.M.R. That’s what we do.”

The comment stands in stark contrast to Mr. Kennedy’s past advice, and senators wondered aloud why he hasn’t told the public what he said on Capitol Hill this week. Last week, he conceded the measles vaccine is “safe and effective” for most people.

When measles broke out in Texas last year, Mr. Kennedy did not recommend vaccination; he said it should be “a personal choice.” Last year, asked if he would advise parents to vaccinate newborns, he said it was not up to him to provide medical advice. His advice, he said, was: “Do your own research.”

But even as he shifted on measles, Mr. Kennedy stuck by his longstanding assertion that improvements in hygiene and sanitation, and not vaccination, fueled the decline in deaths from infectious diseases during the 20th century.

“If you want to talk about what, why disease mortality has disappeared in the 20th century, it was not vaccines,” he said, testifying before the Senate health committee Wednesday afternoon.

As proof, Mr. Kennedy cited a study published in the journal Pediatrics in 2000. But he failed to note that the study also reported that vaccines introduced in the second half of the 20th century had “virtually eliminated” deaths from diseases including polio and measles. In 1999, the Centers for Disease Control and Prevention listed vaccination as one of “ten great public health achievements” of the 20th century.

After Mr. Kennedy made the assertion, Senator Bill Cassidy, the Republican chairman of the Senate health committee, asked about the author of the study; Mr. Kennedy gave him the author’s name. Later in the hearing, Mr. Cassidy produced the paper and told Mr. Kennedy he had taken it out of context.