Trump's vaccine order would require millions of individual shots last used decades ago

WASHINGTON (AP) — Public health experts have been quick to condemn an executive order from President Donald Trump aimed at upending childhood vaccinations in the U.S., but the biggest obstacles may be the unprecedented financial and logistical challenges it would impose on parents, health providers and drugmakers.

WATCH: Trump signs executive order on childhood vaccine recommendations

Monday's announcement by the Republican president calls for separating combination shots — including the measles, mumps and rubella, or MMR, vaccine — into separate injections. Appointments for that and other vaccinations should be spaced out whenever possible, the order states.

To accomplish that, drugmakers would need to revive a slate of individual vaccines that have not been widely used in the U.S. for decades. They would also have to build new manufacturing plants capable of producing millions more vaccine doses than the nation currently uses.

For parents, unbundling the MMR vaccine and spacing out the shots would mean returning to the doctor's office many more times than is currently needed. Those appointments could also strain pediatricians who typically administer the shots, while driving up costs tied to syringes and other medical supplies.

Studies in the U.S. and other countries have shown that combination vaccines increase the likelihood that children will be fully protected from infectious diseases before starting school.

"We do things that are less convenient and more expensive if there's a good reason to do it," said Dr. Anna Durbin, of the Johns Hopkins Bloomberg School of Public Health. "There is no good justification for this. I think it's very bad public health policy."

Under Trump's executive order, federal officials are instructed to develop within 90 days plans for breaking up the MMR shot and spacing out other vaccines.

But pharmaceutical scientists and former regulators say those changes would likely take years and require drugmakers to spend tens of millions of dollars on new studies and manufacturing facilities.

Currently, there are no individual vaccines in the U.S. for measles, mumps or rubella. All the vaccines approved for those viruses by the Food and Drug Administration are combination shots. That three-in-one approach has been the standard in the U.S. since the 1970s.

Dr. Jesse Goodman, a former FDA vaccine chief, said companies may have to conduct large studies showing their new individual shots produce immune system-boosting reactions in children similar to the current versions. The specifics would depend upon the quality of data from the original standalone vaccines and how it's viewed by FDA regulators.

"The question is how much has changed since then and how comfortable will the FDA and the companies be relying on those comparisons?" said Goodman, who is now a professor at Georgetown University.

Manufacturers may also have to demonstrate the safety of new manufacturing facilities and procedures, given that individual measles shots haven't been widely produced in the U.S.