President Donald Trump signs an executive order that calls for changes to the U.S. childhood vaccination schedule, including recommending that the combined measles, mumps and rubella (MMR) vaccine be split into three separate injections given during separate medical visits. The order also directs federal planning aimed at revising timing and reducing the number of universally recommended vaccines.

Multiple outlets report that public health experts say the scientific justification is lacking and that the approach would create major practical barriers. Because stand-alone measles, mumps, and rubella vaccines are not licensed in the U.S. and have not been produced there for decades, manufacturers would likely need new studies and new manufacturing capacity, potentially taking years and tens of millions of dollars. Parents could also face more appointments—potentially more than six visits if MMR is separated and spaced—raising the risk of missed shots and additional costs.

Outlets also note differences in focus: some emphasize expected effects on families and uptake rates, while others stress the order’s limits. Experts interviewed by outlets say the executive action cannot force drug companies to develop new products, and states control school vaccination requirements, meaning any real-world change would depend on state decisions and federal guidance.