By Adam Cancryn, Sarah Owermohle, CNN

(CNN) — President Donald Trump signed an executive order on Monday aimed at reshaping the federal government’s approach toward childhood vaccines, insisting that infants should receive fewer immunizations over a longer period despite little scientific evidence supporting such sweeping changes.

The wide-ranging order proposes reducing the total number of immunizations recommended for children in their earliest years and dividing the nation’s childhood vaccine schedule into three categories.

It also advises that the mumps, measles and rubella (MMR) vaccine be separated into three individual shots — a dramatic change that goes against broad scientific consensus but is in keeping with Trump’s insistence in recent months that the widely administered shot be altered.

The administration signaled that it will push states to rework their vaccine requirements to incorporate the new federal guidelines, effectively upending longstanding practices aimed at improving childhood immunization rates.

“We’re reducing them,” Trump said from the Oval Office. “It’s not only that you’re doing fewer vaccines, or jabs, as they say, but you’re doing them in a series of visits to the doctor.”

Flanked by an array of top health officials, including US Health and Human Services Secretary Robert F. Kennedy Jr., Trump made a range of misleading and incorrect claims about vaccines, including suggesting at one point that the MMR shot can be “quite lethal.”

He alleged repeatedly and without evidence that children were being injected with more vaccines than they could handle, arguing that the shots should be spaced further apart. Pressed on his reasoning for recommending that infants receive their shots over five separate doctor visits, Trump said he’d done it with his children and “had no problem.”

“Nothing bad can happen from what we’re doing,” he said of changes that health experts have long warned will reduce immunization rates and leave children more susceptible to disease. “Nothing bad can happen.”

GOP Sen. Bill Cassidy, a doctor who expressed hesitancy last year over confirming Kennedy to the HHS post due to his positions on vaccines and autism, immediately criticized the order.

“This executive order is wrong. The President does not have the expertise to make these changes. Vaccines are overwhelmingly safe. Vaccines are effective. Vaccines DO NOT cause autism,” Cassidy wrote on X. “Breaking up vaccines will mean children have to get more shots to get the same protection, not fewer shots. It will increase hesitancy and make children less safe.”

Under the order, the administration’s new policy states that all children are recommended to receive vaccines for measles, mumps, rubella, diphtheria, tetanus, pertussis, polio, Hib, pneumococcal disease, HPV and varicella, or chicken pox.

Only high-risk populations are now advised to receive respiratory syncytial virus (RSV) monoclonal antibodies and vaccines against hepatitis A, hepatitis B, meningococcal B, meningococcal ACWY and dengue. That marks a change from the current schedule, which recommends that all children receive most of those shots.

Several of those, such as the hepatitis immunizations, would be based on what’s called shared decision-making, or conversations with a healthcare provider. Those also include shots for rotavirus, meningococcal disease, influenza and Covid-19.

The administration’s new guidance suggests that that the immunizations be given over several medical visits “to give parents more options regarding the timing and frequency” of administration. But Trump offered a far blunter explanation from the Oval Office: He didn’t believe that the current regimen was safe.

“Very simply: Large amounts of vaccine, large amounts of — like vats — of vaccine are currently pumped into your child’s body,” Trump said, at another point comparing the amount of vaccine given to children as “the size of a bottle of soda.”

“We’re doing 20% of that at each visit, and we’ll let time elapse between visits so the body can handle this massive amount of fluid being pumped in,” he said.

There is no evidence to support Trump’s claims.

Trump’s announcement hews closely to an HHS effort in January to whittle down the number of recommended vaccines in the childhood schedule. Medical groups sued to challenge that revised schedule, and a judge ruled in their favor, writing in his opinion that there are “glaring gaps” in expertise among the people Kennedy named to an independent advisory panel on vaccines last year.

Referencing that earlier effort, White House adviser Heidi Overton said Monday that administration officials “are going to be working directly with states so that we’re not reliant on the court case to resolve. We are doing it right away so that parents get the benefit from state laws changing.”

The vaccine announcement came shortly after Senate Republicans released 2021 text messages obtained from Dr. Anthony Fauci’s government phone showing the former top health official discussing possible risks of the Covid-19 vaccine to pregnant women. Later studies showed that the vaccines were safe during pregnancy.

Asked about a push by Republican senators for the Justice Department to charge Fauci with contempt of Congress, Trump said he’d yet to talk about it with US Attorney for the District of Columbia Jeanine Pirro.

The Monday order on vaccines followed months of escalating pressure that Trump had put on Kennedy for more action on the childhood vaccine schedule, as the two men both publicly speculate about links between vaccines and autism.

There have been extensive scientific studies of vaccines that have yielded no evidence of a connection to autism.

It also came despite long-running reservations among Trump’s political advisers that advancing controversial vaccine policies is widely unpopular and could alienate voters ahead of November’s midterms.

White House officials earlier this year urged Kennedy to shift his focus to other, more mainstream initiatives due to concerns about the political fallout, though his department’s work on vaccines has continued in the background.

“This is something very important for all of us,” Trump said. “Very happy to sign it.”

Yet questions swirled Monday about the mechanics of separating out the measles, mumps and rubella vaccines, particularly because those are not sold separately in the US market.

HHS is working with the private sector to make those commercially available, and Kennedy is expected to produce a plan for separate vaccines within 90 days, a White House official said Monday.

“The president has long held that the MMR vaccine should be separated and wants that available as an option,” the official said.

Another White House official said, “This isn’t just the president …arbitrarily setting vaccine policy.” The official pointed to a January scientific assessment that HHS carried out before unveiling the proposed schedule that was eventually blocked in court.

That assessment does not specifically address the utility, safety or effectiveness of separating the measles, mumps and rubella shots.

Concerns spiked Monday among pediatricians and medical groups that removing broad recommendations for certain childhood vaccines could mean out-of-pocket costs for parents who do want to fully vaccinate their children.

By law, insurers must cover without cost to patients the vaccines that are recommended by the US Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices, the panel of experts who Kennedy replaced last year.

The new contingent on the panel, some of whom have stated objections to vaccines, has already discussed delaying hepatitis B vaccination from infancy to 12 years of age. The changes ordered by Trump on Monday would recommend hepatitis immunizations only for high-risk populations.

“They still are a recommendation, and so we assume that that means they’ll still be covered by insurance and fully available to parents that want them,” the first official said Monday.

This story has been updated with additional reporting and developments.