WASHINGTON - When Health and Human Services Secretary Alex Azar announced this week that the federal government would begin releasing coronavirus vaccine doses that had been held in reserve for second shots, no such reserve existed, according to state and federal officials briefed on distribution plans. The Trump administration had already begun shipping out what was available, starting at the end of December, taking second doses for the two-dose regimen directly off the manufacturing line.

Now, health officials across the country who had anticipated their extremely limited vaccine supply as much as doubling beginning next week are confronting the reality that their allocations will remain largely flat, dashing hopes of dramatically expanding access for millions of elderly people and those with high-risk medical conditions. Health officials in some cities and states were informed in recent days about the reality of the situation, while others were still in the dark Friday.

Because both of the vaccines authorized for emergency use in the United States are two-dose regimens, the Trump administration's initial policy was to hold back second doses to protect against manufacturing disruptions. But that approach shifted in recent weeks, according to the officials, who spoke on the condition of anonymity because they were not authorized to discuss the matter.

Operation Warp Speed, which is overseeing vaccine distribution, stopped stockpiling second doses of the Pfizer-BioNTech vaccine at the end of last year, those officials were told. Shipping of the last reserve doses of Moderna's supply, meanwhile, began over the weekend.

The shift, in both cases, had to do with increased confidence in the supply chain, so Operation Warp Speed leaders felt they could reliably anticipate the availability of doses for booster shots - required three weeks later in the case of the Pfizer-BioNTech product and four weeks later under Moderna's protocol.

But it also meant there was no stockpile of second doses waiting to be shipped, as Trump administration officials suggested this week. Azar, at a briefing Tuesday, said, "Because we now have a consistent pace of production, we can now ship all of the doses that had been held in physical reserve." He explained the decision as part of the "next phase" of the nation's vaccination campaign.

Those in line for their second shots are still expected to get them on schedule because second doses are prioritized over first shots and states are still receiving regular vaccine shipments. But state and local officials say they are angry and bewildered by the shifting directions and changing explanations about supply. Their anxiety was deepened by projections that a highly contagious virus variant would spread rapidly throughout the United States and as daily covid-19 deaths averaged 3,320 this week.

The health director in Oregon, Patrick Allen, was so disturbed that he wrote Azar on Thursday demanding an explanation. In his letter, he recounted how Gustave Perna, the chief operating officer of Operation Warp Speed, had "informed us there is no reserve of doses, and we are already receiving the full allocation of vaccines."

"If true, this is extremely disturbing, and puts our plans to expand eligibility at grave risk," Allen wrote. "Those plans were made on the basis of reliance on your statement about 'releasing the entire supply' you have in reserve. If this information is accurate, we will be unable to begin vaccinating our vulnerable seniors on Jan. 23, as planned."

HHS spokesman Michael Pratt confirmed in an email that the final reserve of second doses had recently been released to states but did not address Azar's comments, saying only, "Operation Warp Speed has been monitoring manufacturing closely, and always intended to transition from holding second doses in reserve as manufacturing stabilizes and we gained confidence in the ability for a consistent flow of vaccines."

But the explanations by the federal government were conflicting. The 13 million doses made available for states to order this week - for delivery next week - represented "millions more" than in previous weeks, Pratt said. He also said states have not requested the full amount they have been allocated.

Guidance circulated Friday among HHS officials acknowledged, however, that "the notion that there is a large bolus of second doses that will be released to jurisdictions is not accurate." And state and municipal health officials said their allocations for next week had increased only marginally, if at all.

Chicago Public Health Commissioner Allison Arwady said her city's share had gone from about 32,000 doses to 34,000 doses. "I have stopped paying a whole lot of attention to what is being said verbally at the federal level right now," she said.

Nirav Shah, the director of Maine's Center for Disease Control and Prevention, said he learned only Friday, by calling his state's designated contact at Warp Speed, that the reserve no longer existed.

Maine still plans to broaden vaccination next week to those 70 and older. "Who is in line will not change," Shah said. "The velocity of that line will change because this bolus of doses that we intuited was coming based on Azar's comments is not coming."

In an email that reached some state officials Friday morning, Christopher Sharpsten, an Operation Warp Speed director, called it a "false rumor" that "the federal government was holding back vaccine doses in warehouses to guarantee a second/booster dose."

In fact, that information had come fromAzar, who said Tuesday that the "next phase" of the country's vaccination campaign involved "releasing the entire supply we have for order by states, rather than holding second doses in physical reserve."

Azar's comments Tuesday followed a Jan. 8 announcement by President-elect Joe Biden's transition team that his administration would move to release all available doses rather than holding half in reserve for booster shots. Biden's advisers said the move would be a way to accelerate distribution of the vaccine, which is in short supply across the country.

Azar initially said the Biden plan was shortsighted and potentially unethical in putting people at risk of missing their booster shots. When he embraced the change four days later, however, he did not say that the original policy had already been phased out or that the stockpile had been exhausted. Trump administration officials and Biden's team alike have sought to reassure the public that increasing the pace of immunizations would not endanger booster shots.

Azar also signaled to states that they would soon see expanded supply, urging them to begin vaccinating adults 65 and older and those under 64 with high-risk medical conditions. Officials in some states embraced that directive, while others said that suddenly putting hundreds of thousands of additional people at the front of the line would overwhelm their capacity.

In subsequent conversations with state and local authorities, federal officials sought to temper those instructions, said people who participated in the conversations. Perna, for instance, spoke directly to officials in at least two of the jurisdictions receiving vaccine supply, explaining that allocations would not increase and that they did not have to broaden eligibility as they had previously been told, according to a health official who was not authorized to discuss the matter.

The revised instructions led some state and local officials to hold off on changes. One state health official noted that the updated eligibility guidance announced Tuesday did not appear on the website of the CDC, even though it was stated as federal policy by Azar and by Robert Redfield, the CDC director, in their remarks. Under the original recommendations, adults 65 and older and front-line essential workers were to comprise the second priority group, known as Phase 1b, after medical workers and residents and staffers of long-term-care facilities.

There was additional confusion from another change Azar announced this week - making allocation of doses dependent on how quickly states administer them. He originally said that would not take effect for two weeks.

But Connecticut Democratic Gov. Ned Lamont on Thursday tweeted that federal officials had notified him thatthe state would receive an additional 50,000 doses next week "as a reward for being among the fastest states" to get shots into arms. West Virginia, meanwhile, which is moving at the fastest clip, according to CDC data, did not get any additional doses, said Holli Nelson, a spokeswoman for the state's National Guard.

In a sign that the incentive structure may not be long-lived, a senior Biden transition official, speaking on the condition of anonymity to address ongoing deliberations, said this week that the team did not look kindly on a system that "punishes states."

Biden has said he wants to see 100 million shots administered within his first 100 days - an aim that will depend on quickly accelerating the pace of immunization. Together, Pfizer and Moderna have agreed to sell 200 million doses to the United States by the end of March, which is enough to fully vaccinate 100 million people.