Plans by U.S. President Joe Biden’s administration to go forward with a nationwide vaccine booster program are being scaled back over concerns related to the Moderna vaccine and internal disagreements. Sources told CNN that there are ongoing internal deliberations within the administration.

Whether or not to go ahead and encourage vaccinated Americans to seek a booster has gathered urgency amid the spread of COVID-19’s Delta variant. Infections and hospitalizations are steadily rising across the U.S., including among vaccinated Americans, and the question has gravitated towards the possibility of a booster shot. Dr. Anthony Fauci, the nation’s top infectious disease expert, recently warned that a third shot may be likely in the future.

However, the implementation of a booster plan has been complicated by issues related to data on boosters and bureaucratic disagreements.

Currently, the administration's Pfizer/BioNTech COVID-19 vaccine booster plan remains on track for the week of September 20, but it will take longer for boosters to go-ahead for the Moderna vaccine. Federal health officials warned that Moderna's submission for the booster was found to be “inadequate” and “strengthened data" was needed from the company.

But there are also disagreements between the White House and federal health agencies on the implementation schedule. Officials from the Food and Drug Administration (FDA) and the Center for Disease Control (CDC) warned the White House that they disagreed with any specific date for when Americans should expect to begin receiving boosters. However, they felt that their advice was being ignored by officials. The FDA’s acting commissioner Margaret Woodcock displayed a degree of frustration about the schedule announcement in a recent interview.

"Why would you announce this? Well, we need to have a plan and the plan would involve the vaccination of very large numbers of people in the United States with a booster dose," Woodcock told Dr. John Whyte said in a recent interview.

White House officials admitted that they were waiting for sign off from the public health agencies. A White House spokesperson repeated that the administration will continue to"follow the science".

“When that approval and recommendation are made, we will be ready to implement the plan our nation's top doctors developed so that we are staying ahead of this virus,” Chris Meagher said in a statement on Friday.