The White House on Wednesday defended the administration's COVID-19 booster vaccine plan as the US Food and Drug Administration (FDA) announced the resignations of two top vaccine officials amid reports they are leaving because the plan was rolled out before officials had a chance to approve it.

The booster decision is based on "mountains and mountains of available data on vaccine effectiveness" reviewed by the nation's leading public-health officials, White House press secretary Jen Psaki said at a briefing. Those top public-health officials "made a critical judgement that boosters will be needed", she said.

The FDA announced on Tuesday that Marion Gruber, who leads the Office of Vaccines Research and Review, will depart the FDA at the end of October. Her deputy, Philip Krause, will leave the agency in November, BioCentury reported. Gruber has been at the FDA for more than 30 years, and Krause for more than a decade.

In a letter announcing the resignations obtained by the biotech-industry publication Endpoints, Dr Peter Marks, the director of the FDA's Center for Biologics Evaluation and Research, praised the pair for their work during the COVID-19 pandemic. He didn't give a reason for their departures.

The administration announced last month that most people would be offered a COVID-19 booster shot about eight months after vaccination.

A former FDA official, who wasn't identified by name, told Politico that the resignations were tied to anger over the FDA's lack of autonomy in booster planning, while a current official, also not named, told the news outlet that the pair were leaving over differences with Marks.

Jeff Zients, the White House's coronavirus czar, said Wednesday the decision to start booster shots "was made by and announced by the nation's leading public-health officials" including the acting FDA commissioner, the Centers for Disease and Prevention (CDC) director, the surgeon general, the director of the National Institutes of Health and others.

"Having reviewed all of the available data, it is in their clinical judgment that it is time to prepare Americans for a booster shot," Zients said.

He said the administration had "also been very clear throughout that this is pending the FDA conducting an independent evaluation and CDC's panel of outside experts issuing a booster dose recommendation".

The FDA — and its vaccine office — has been at the center of the government's effort to speed coronavirus vaccines and other therapies. The agency remains under considerable pressure to approve vaccines for children under age 12, a decision that probably remains months away.

FDA officials are also scrambling to collect and analyze data that clearly demonstrate the boosters' benefits before the administration's Sept 20 deadline for rolling them out to most adults, Politico reported.

Many outside experts, and some within the agency, see uncomfortable similarities between the Biden team's top-down booster plan and former President Donald Trump's attempts to goad FDA into accelerating its initial authorization process for Covid-19 vaccines and push through unproven virus treatments, according to Politico.

The World Health Organization has repeatedly urged wealthy nations to hold off on booster shots of the coronavirus vaccines until people in poorer countries can get their first doses.

FDA officials said Tuesday that the officials' departures wouldn't hamper the agency's work.

"We are confident in the expertise and ability of our staff to continue our critical public health work, including evaluating COVID-19 vaccines," FDA spokeswoman Stephanie Caccomo said in a statement.