President-elect Donald Trump’s choice for health secretary has suggested that the polio vaccine cost more lives than it saved and that the vaccine did not wipe out the disease in the U.S.

Robert F. Kennedy Jr. is trying to tamp down concerns about his history of vaccine skepticism as he meets with GOP senators who will vote on whether to confirm him as President-elect Donald Trump’s pick to lead the US Department of Health and Human Services.

Attorney Aaron Siri filed the petition on behalf of Informed Consent Action Network, a group that questions vaccine safety. The petition criticizes the clinical trials done to license the polio vaccine manufactured by Sanofi Pasteur and argues it should not be administered until another trial is conducted.