The Food and Drug Administration late Monday shot down an idea floated by a top Trump administration vaccine official who proposed halving doses of the Moderna vaccine. The FDA said that the proposal to stretch the Moderna vaccine was “premature and not rooted solidly in the available science.”

“We want to remind the public about the importance of receiving COVID-19 vaccines according to how they’ve been authorized by the FDA in order to safely receive the level of protection observed in the large randomized trials supporting their effectiveness,” the agency said in a statement posted to its website on Monday night. 

The statement came after Moncef Slaoui, the chief science adviser for Operation Warp Speed, said on Sunday that federal officials and Moderna were discussing the possibility of cutting each of Moderna’s required two doses in half — going against the vaccine’s stated requirements for use and giving each recipient the equivalent of a single dose.

Slaoui suggested on Sunday that Moderna’s clinical trial data revealed that people between the ages of 18 and 55 who received two 50-microgram doses showed an “identical immune response” to the two required 100-microgram doses.

But the FDA’s statement a day later criticized Slaoui’s assertion as too hasty given a lack of available evidence to justify hollowing out the doses.

“We have been following the discussions and news reports about reducing the number of doses, extending the length of time between doses, changing the dose (half-dose), or mixing and matching vaccines in order to immunize more people against COVID-19,” the statement said.

The FDA insisted that any changes to the vaccine regimen would require research in additional clinical trials before being approved or adopted noting that sudden ad hoc adjustments “run a significant risk of placing public health at risk, undermining the historic vaccination efforts to protect the population from COVID-19.” 

The statement noted that clinical trial recipients of the Moderna or Pfizer-BioNTech vaccine who did not receive two doses at the proper time “were generally only followed for a short period of time,” making it inadvisable to draw conclusions about the depth or duration of protection from a single dose of the vaccines.

Dr. Anthony Fauci said on Monday that the sudden switch could also “confuse the public” amid an effort to The  top infectious diseases expert said during an interview with The New York Times that the effort to spread the doses was misdirected after reports that states have not yet vaccinated people with existing doses of the approved coronavirus vaccines.

“At the present time we are not dealing with a shortage of doses — we are dealing with the need to increase our efficiency in getting people vaccinated,” Fauci said.