Senior officials of the World Health Organization, including Director-General Tedros Adhanom Ghebreyesus, criticized the Trump administration’s newest attempt to trigger an overhaul of U.S. vaccination policy on Wednesday, calling it politically motivated and contradictory to the best available science.

The critique was aimed at an executive order signed by President Trump on Monday. It calls for a reduction in the number of vaccinations recommended for all children in the U.S., and for the use of vaccines targeting single pathogens rather than the combination vaccines now in use, starting with the measles, mumps, and rubella shot.

The changes being pushed by the executive order are predicated on the disproven claim that the increased use of vaccines is behind the rising rates of autism in the U.S.

“Vaccines, including the MMR vaccine, are safe, and do not cause autism,” Tedros said during a press conference. “Delaying vaccines or separating doses unnecessarily does not make vaccinations safer and can leave children unprotected.”

“Vaccination policy should be guided by rigorous, independent, and transparent review of the best available science and not by political influence,” the director-general said.