WASHINGTON -- As demand for COVID-19 vaccines declines across the United States, unused Johnson & Johnson vaccine doses may have to go to waste, an NBC News report said on Wednesday.

The buildup of doses is largely a result of the Food and Drug Administration's order in early April pausing distribution of the Johnson & Johnson vaccine because of safety concerns, the report said.

The report noted that there are also concerns over the lack of a coordinated federal plan to redistribute them.

Andy Slavitt, who just stepped down from the White House COVID-19 Response Team on Wednesday, put some of the responsibility for getting the unused doses into arms on the states, and said Tuesday at a briefing that "a very small fraction of doses that have been sent out to states" are at risk of expiring, according to the NBC.

The vaccine is estimated to be viable for up to three months at normal refrigerated temperatures, according to Johnson & Johnson, although it is stable for two years if frozen.