President Donald Trump signed an executive order on Monday that seeks to change childhood vaccine recommendations, endorsing his long-held but discredited theory that vaccines cause autism. The order calls for the measles, mumps and rubella (MMR) vaccine to be split into three separate single-disease shots and for all childhood immunizations to be given at separate appointments whenever possible. It also directs the nation's health department to carry out the changes. The order goes against the guidance of medical groups, which consider the theory a myth. The order could dramatically overhaul how parents and children receive and regard scientifically proven vaccines for a wide array of diseases.