WASHINGTON (AP) — President Donald Trump on Monday signed an executive order calling for revamped childhood vaccine recommendations that promote his long-held but discredited theory that childhood shots should be spaced out into separate medical visits. Childhood vaccines — and how and when to give them in combination — go through rigorous studies, and safety tracking continues for years as the shots are used. Even as the order calls for revised vaccine recommendations, states, not the federal government, have the authority to require vaccinations for schoolchildren. Changes to federal childhood vaccine recommendations customarily require approval from the director of the Centers for Disease Control and Prevention. Scientific consensus and decades of studies have firmly concluded there is no link between childhood vaccines and autism.