An increasing number of COVID-19 vaccination sites around the U.S. are canceling thousands of appointments because of vaccine shortages in a rollout so rife with confusion that even the new CDC director admitted she doesn't know exactly how many shots are in the pipeline.

States waited to find out their latest weekly allocation of vaccine from the federal government on Tuesday amid complaints from governors and top health officials about inadequate supplies and the need for earlier and more reliable estimates of how much is on the way so that they can plan accordingly.

President Joe Biden suggested Monday that he hopes the country can soon ramp up to 1.5 million shots dispensed per day. His administration has also promised more openness and said it will hold news briefings three times a week about the outbreak that has killed over 420,000 Americans.

Amid the rising frustration, the Biden White House scheduled its first virus-related call with the nation's governors Tuesday. The president planned to give an update on efforts to bolster the vaccine supply and put more shots into Americans' arms more quickly, press secretary Jen Psaki said.

The setup inherited from the Trump administration has been marked by miscommunication and unexplained bottlenecks, with shortages reported in some places even as vaccine doses remain on the shelf.

Dr. Rochelle Walensky, Biden's brand-new director of the Centers for Disease Control and Prevention, was herself flummoxed over the weekend in trying to describe current supplies.

"I can't tell you how much vaccine we have," she told "Fox News Sunday," describing the problem as a challenge left by the outgoing Trump administration. "And if I can't tell it to you, then I can't tell it to the governors, and I can't tell it to the state health officials. If they don't know how much vaccine they're getting, not just this week, but next week and the week after, they can't plan."

On Monday, Florida Gov. Ron DeSantis said the state is "at the mercy of what the federal government sends us" and can't meet growing demand from residents.

Officials in West Virginia, which has had one of the best rates of administering vaccine, said they have fewer than 11,000 first doses on hand even after this week's shipment.

"I'm screaming my head off" for more, Republican Gov. Jim Justice said.

Georgia Gov. Brian Kemp said he doesn't expect the state's allotment to increase in the coming weeks, which will limit progress in vaccinating those now eligible, including people over 65 and first responders. Rhode Island officials said late last week that they can't expand eligibility to those over 65 at current allocations, despite complaints from advocates for the elderly.

The weekly allocation cycle for first doses begins on Monday nights, when federal officials review data on vaccine availability from manufacturers to determine how much each state can have. Allocations are based on each jurisdiction's population of people 18 and older.

States are notified on Tuesdays of their allocations through a computer network called Tiberius and other channels, after which they can specify where they want doses shipped. Deliveries start the following Monday.

A similar but separate process for ordering second doses, which must be given three to four weeks after the first, begins each week on Sunday night.

As of Tuesday morning, the CDC reported that just over half of the 41 million doses distributed to states have been put in people's arms. That is well short of the hundreds of millions of doses that experts say will need to be administered to achieve herd immunity and conquer the outbreak.

The U.S. ranks fifth in the world in the number of doses administered relative to the country's population, behind No. 1 Israel, United Arab Emirates, Britain and Bahrain, according to the University of Oxford.

The reason more of the available shots in the U.S. haven't been dispensed isn't entirely clear. But many vaccination sites are apparently holding large quantities of vaccine in reserve to make sure people who have already gotten their first shot receive the required second one on schedule.

Also, some state officials have complained of a lag between when they report their vaccination numbers to the government and when the figures are posted on the CDC website.

In the New Orleans area, Ochsner Health said Monday that inadequate supply forced the cancellation last week of 21,400 first-dose appointments but that second-dose appointments aren't affected.

Inova Health System, the largest health provider in Virginia's Washington, D.C., suburbs, said it is canceling all first-dose appointments at its mass vaccination clinics beginning Thursday because of inadequate supplies. Second-dose appointments will be honored.

In North Carolina, Greensboro-based Cone Health announced it is canceling first-dose appointments for 10,000 people and moving them to a waiting list because of supply problems.

Jesse Williams, 81, of Reidsville, North Carolina, said his appointment Thursday with Cone Health was scratched, and he is waiting to hear when it might be rescheduled. The former volunteer firefighter had hoped the vaccine would enable him to resume attending church, playing golf and seeing friends.

"It's just a frustration that we were expecting to be having our shots and being a little more resilient to COVID-19," he said.

The vaccine rollout across the 27-nation European Union has also run into roadblocks and has likewise been criticized as too slow. Pfizer is delaying deliveries while it upgrades its plant in Belgium to increase capacity. And AstraZeneca disclosed that its initial shipment will be smaller than expected.

The EU, with 450 million citizens, is demanding that the pharmaceutical companies meet their commitments on schedule.

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Associated Press writers around the U.S. contributed to this report.

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Find AP's full coverage of the coronavirus pandemic at https://apnews.com/hub/coronavirus-pandemic