By Ahmed Aboulenein

WASHINGTON, Sept 24 (Reuters) - Dr. Heidi Overton, President Donald Trump's pick to lead the embattled US FDA, told senators on Thursday that all vaccines on the US market are safe and effective, as the health committee's Republican chairman pressed her on immunization at ‌her confirmation hearing.

In his opening statement, US Senator Bill Cassidy of Louisiana pressed Overton to affirm the safety of the measles, mumps and ‌rubella vaccine and to commit to keeping politics out of the agency's decisions.

He criticized Overton for standing behind Trump when the president signed an executive order breaking up the childhood vaccine schedule into ​more doses, a move physicians' groups and vaccine makers strongly oppose. Cassidy, himself a physician, said the order was based on "zero scientific evidence" and would raise costs for families.

Cassidy, noting Overton's presence...