WASHINGTON (AP) — Senior U.S. officials will begin receiving coronavirus vaccines this week as part of updated federal continuity of government plans that now include terrorism and pandemics as threats to the nation, and its leaders.

The effort comes after President Donald Trump tweeted on Sunday that White House aides should receive the COVID-19 vaccine "somewhat later in the program." Still, doses are expected to be administered at the White House, Capitol Hill and other facilities within the week, according to senior administration officials.

Trump's statement about moving more slowly was only expected to affect priority vaccination for a small subset of the hundreds, if not more, officials who are to be inoculated with the Pfizer vaccine, which received emergency use authorization from the Food and Drug Administration on Friday.

Public distribution of the shot is initially limited to front-line health workers and people in nursing homes and long-term care facilities

The exact number and role of officials set to receive the vaccine is classified, according to senior administration officials. It is not expected to include Trump and Vice President Mike Pence themselves at this point. Lawmakers on Capitol Hill have yet to be informed how many doses they will receive and have yet to develop a vaccination plan, one official said.

The full rollout is being coordinated by the National Security Council, officials said, in concert with the White House Medical Unit, the Department of Homeland Security, the Office of Management and Budget and the Department of Health and Human Services.

"Senior officials across all three branches of government will receive vaccinations pursuant to continuity of government protocols established in executive policy," National Security Council spokesperson John Ullyot said Sunday. "The American people should have confidence that they are receiving the same safe and effective vaccine as senior officials of the United States government on the advice of public health professionals and national security leadership."

The move to vaccinate top U.S. officials would be consistent with the earlier rollout of rapid testing machines for the coronavirus, which were similarly controlled by the federal government with kits reserved to protect the White House complex and other critical facilities.

The government vaccination program is being conducted under the authority of a classified "National Continuity Policy" signed by President Barack Obama called Presidential Policy Directive-40, the most recent government-wide planning document for a range of worst-case scenarios.

Over the past decades, Cold War-era plans for nuclear war have been updated to account for new threats, including terrorism, cyberwarfare and even pandemics.

The directive requires agencies to take steps to ensure continuity of operations, the executive branch to ensure the continuity of government, and cooperation with the legislative and judicial branches to ensure "Enduring Constitutional Government." Officials said that vaccinating critical staff would reduce the risk of staffing shortages in key roles due to illness or quarantine and ensure essential government services could continue.

Among those expected to receive initial doses are military aides to the president, Situation Room watch officers, Secret Service agents. Quarantines for exposure to the virus have proven to be particularly challenging to those essential government functions.

According to guidance from the Centers for Disease Control and Prevention, there is not yet enough information to determine whether those who have had COVID-19, like Trump, should also get the vaccine.

Pence has not contracted the virus, and his aides have been discussing when and how he should receive the vaccine as the administration looks to boost public confidence in the shot.

Other government officials, including Health and Human Services Secretary Alex Azar, were holding events Monday to celebrate the vaccine and to attempt to raise public awareness about its efficacy and safety.

Aides to President-elect Joe Biden have been discussing when and how he should receive the vaccine and have been working to establish plans to boost virus safeguards in the West Wing to keep the 78-year-old Democrat healthy after he takes office They are also examining whether those who work in close contact with Biden should also be vaccinated ahead of his Jan. 20 inauguration.

Biden said earlier this month that he wants take the vaccine in public under guidance of his chief medical adviser, Dr. Anthony Fauci. He also alluded in a CNN interview to polling that suggests "people have lost faith in the ability of the vaccine to work."

The president-elect has since been consulting with Fauci about when he should be vaccinated as he looks to help aid public health experts' efforts to build confidence in the vaccination, according to a Biden transition official who spoke on condition of anonymity because the official was not authorized to comment publicly. The official added that Biden remains committed to taking the vaccine in public.

At the same time, Biden also has publicly stressed that he wants to make certain that front-line health care workers and the most vulnerable are at the front of the line, a dynamic that could have some impact on the timing of when White House staff are vaccinated.

"We will follow the guidance of scientists and get vaccines to those most at-risk," Biden said last week. "That includes health care personnel and people in long-term care; and, as soon as possible, that will include educators."

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AP writers Lisa Mascaro in Washington and Aamer Madhani in Wilmington, Delaware contributed.