Doctors worry that President Donald Trump’s new executive order on vaccines will stoke fear and confusion among parents at a time when measles is raging, immunization rates are falling and children are heading back to school. The order advocates separating the measles, mumps and rubella vaccine into three different single-disease shots and giving all childhood immunizations at separate appointments when possible. It also includes several changes to the childhood vaccine schedule already attempted by Trump’s health department, which have been blocked by a federal judge. Doctors say the recommendations are not based on science and worry they will worsen vaccine hesitancy and endanger kids.