Federal and state officials didn’t provide an explanation Thursday for why Maine was told it will receive about one-third of the doses that it was expecting in the initial shipment of the first COVID-19 vaccine.

Officials with the U.S. Department of Health and Human Services, which is overseeing the vaccine rollout, didn’t respond to multiple requests for an interview a day after Gov. Janet Mills said she was alarmed by the apparent shortage of COVID-19 vaccine doses for Maine.

Spokespeople for Sens. Susan Collins, a Republican, and Angus King, an independent, declined to say what the senators were doing to ensure a fair and equitable distribution of the vaccine, and a spokesman for the Maine Center for Disease Control and Prevention said he had no additional information on the matter.

Maine’s congressional delegation is, however, scheduled to update Mills on the vaccine distribution process during a virtual meeting Friday morning.

Mills said Wednesday that federal projections of Maine’s share of initial shipments of the first COVD-19 vaccine expected to be approved by the Food and Drug Administration had been slashed by nearly two-thirds.

Mills said it was “alarming” to see the reduction in anticipated shipments of the Pfizer vaccine, which could begin arriving mid-December.

“Most alarming, the federal government, it appeared to us, significantly reduced the estimate of the number of Maine’s initial allocation of the Pfizer vaccine from around 36,000 to about 12,675 doses,” Mills said in a media briefing Wednesday. “This is far less than what is needed for Maine and proportionally for other states as well.”

Mills said other governors also expressed concern during a conference call about vaccine distribution on Monday with Vice President Mike Pence and U.S. Health and Human Services Secretary Alex Azar. No answers were given for why the vaccine shipment numbers were lower than expected, she said.

The FDA is scheduled to consider emergency use authorization for vaccines from Pfizer on Dec. 10 and from Moderna on Dec. 17, with distribution to states to begin soon after.

Dr. Nirav Shah, director of the Maine CDC, said that “for a brief period” a special online dashboard that the state agency can access showed about 36,000 doses were expected. But the number dropped to 12,675 this week. The dashboard is part of Operation Warp Speed, the name given to the partnership between the federal government and private companies to quickly develop, manufacture and distribute a vaccine.

Shah said it’s possible states will receive smaller but more frequent deliveries of batches of the vaccine that would add up to the amount expected, but he said it’s unknown if that is the federal plan or if there are other issues affecting shipments.

Federal officials said this week that rather than wait until the end of December to distribute a cumulative amount of vaccine, doses that are available earlier will be distributed sooner, followed by additional allocations as more vaccines are certified and approved for distribution.