The federal government is releasing millions of Moderna booster shots that were delayed by the Food and Drug Administration as a result of a safety inspection at an Indiana packaging plant, even as states report shortages and encourage patients to use Pfizer boosters instead.

The release of the withheld vaccines, which has not previously been reported, represents the latest wrinkle in the Biden administration’s fall booster campaign, with officials dealing with slow uptake of the redesigned shots even before President Biden’s message this week that the “pandemic is over.” Only 34.9 percent of eligible Americans ages 5 and older have received a booster shot since the first batch was made available last year, according to federal data, and the White House has been encouraging Americans to seek out updated Moderna and Pfizer shots that are targeted against omicron and its subvariants.

The FDA’s inspection was focused on production issues at a Bloomington, Ind.-based plant operated by Catalent, which is helping to bottle and package Moderna’s vaccine. Inspectors last month began raising concerns the facility was not sufficiently sterile, and checking whether any vials packaged there might have been contaminated, as part of routine safety reviews, said people with knowledge of the inspection. FDA inspectors concluded there were no problems with Moderna’s vaccine, and the agency is set to soon release more than 10 million doses that had been held back.

“On Tuesday, FDA authorized distribution of numerous batches of the updated Moderna COVID-19 Vaccine, Bivalent booster manufactured at Catalent’s facility,” FDA spokesperson Michael Felberbaum said in a statement. “This authorization was based on FDA’s determination that the batches met all applicable specifications, following a careful review of information provided by Moderna about the manufacture of these batches. The agency has no concerns with the safety, effectiveness, or quality of these batches.”

FDA inspectors found no safety issues at a second plant, operated by Thermo Fisher Scientific, which is also working to help finish Moderna’s vaccines for U.S. distribution, officials said.

In a statement, Moderna said that it was “working closely” with the U.S. government to deliver additional doses of its bivalent booster shots – which include components aimed at the latest subvariants as well as the original virus identified in Wuhan, China, which has long since disappeared – amid “high demand” in parts of the country.

“We anticipate that these availability constraints will be resolved in the coming days,” said spokesperson Chris Ridley. “We continue to be on track to meet our committed delivery of 70 million doses of our updated, bivalent vaccine by the end of this year.”

Catalent did not immediately respond to a request for comment.

FDA on Aug. 31 authorized new omicron-targeting coronavirus booster shots from Moderna and Pfizer, with experts saying the shots should improve protection against severe illness and death during a potential increase in COVID-19 cases this fall and winter. But providers around the country have reported shortages of Moderna in recent weeks, prompting state officials to encourage consumers to seek out the alternative.

“If your provider is waiting for Moderna Omicron booster doses, there’s plenty of Pfizer,” Don Herrington, interim director of the Arizona Department of Health Services, wrote in a blog post on Monday. Herrington said that federal officials advised the supply issues would be resolved “in approximately two weeks.”

FDA officials first became aware of potential safety concerns at the Catalent plant in late August, even as the agency was preparing to authorize the new boosters, said three people with knowledge of the inspection who were not authorized to comment. Biden officials have avoided publicly commenting on the Moderna booster delays until the safety inspection was complete amid concerns about undermining vaccine confidence, the people said.

According to FDA, the agency did not initially include the Catalent facility when authorizing the booster shots because of the ongoing safety inspection.

“The inspection of the Catalent facility has now been completed and the investigators have issued a list of observations that pertain to items such as visual inspection processes, investigations, and root cause analyses,” Felberbaum said.

In interviews earlier this month, Biden officials said the holdup with Moderna vaccines would not significantly constrain short-term supply for the booster campaign, since they had already planned to rely on the shots produced by Pfizer and its German partner, BioNTech. The administration earlier this year ordered more than twice as many doses from Pfizer-BioNTech than Moderna for the booster campaign.

It’s unclear whether some patients have a preference for the Moderna shots, said Marcus Plescia, chief medical officer for the Association of State and Territorial Health Officials. “It appears there are adequate supplies of Pfizer to meet current demand,” Plescia added, though he said he was still gathering information from state officials.

The FDA inspection represented another wrench in the vaccine-production process, an issue that occurs with some frequency in the pharmaceutical industry. Problems at a Baltimore plant operated by Emergent, another contract manufacturer, halted production of Johnson & Johnson coronavirus vaccines there last year and prompted government officials to discard millions of doses. Catalent’s Indiana plant has also been faulted by FDA inspectors in a 2018 inspection that found problems with quality control.

Public health experts also expressed concern that Biden’s statement on “60 Minutes,” which aired on Sunday, could be another factor dampening enthusiasm for the booster campaign. While the president acknowledged the nation “still [has] a problem with COVID,” his claim the “pandemic is over” was widely amplified, including by Republicans who asked why the White House is continuing to promote vaccination campaigns if the threat has receded.

“It was an uphill battle already,” said Jennifer Kates, who leads global health policy for the Kaiser Family Foundation, a nonpartisan think tank. “There’s still messaging confusion. People are unclear if they should get a new booster, when should they get the booster … [it’s] a very difficult landscape of trying to help the public understand that these vaccines are safe and effective.”

Kates said that she personally encountered Moderna shortages when she recently went to get a booster shot. “If there are people who have a preference, that’s a wrinkle to them,” she said.

The White House on Tuesday maintained that Biden’s comments on “60 Minutes” were consistent with the administration’s posture that deaths and severe disease from COVID have come down – and can be further reduced with vaccinations.