Jill Biden, left, and Governor Janet Mills, right, pose for a photo following a rally on Tuesday, Oct. 27, 2020, in Bangor, Maine. Credit: Linda Coan O'Kresik / BDN

The administration of President Joe Biden is boosting purchases of coronavirus vaccines to deliver enough to protect 300 million Americans by the end of the summer and surging deliveries to states for the next three weeks following shortages and inconsistent supplies.

The federal government announced the surge Tuesday, along with the news that the federal government is purchasing an additional 100 million doses each of the two approved coronavirus vaccines. With existing purchases, the White House expects to be able to deliver enough of the two-dose regimens to states to vaccinate 300 million people.

The purchases from drugmakers Pfizer and Moderna come as the Biden administration is trying to ramp up vaccine production and states’ capacities to inject them into arms. Even more vaccine could be available if federal scientists approve a single-dose shot from Johnson & Johnson, which is expected to seek emergency authorization in the coming weeks.

Biden also announced a roughly 16 percent boost in deliveries to states over the coming weeks, amid complaints of shortages so severe that some vaccination sites around the U.S. had to cancel tens of thousands of appointments with people seeking their first shot.

Maine Gov. Janet Mills said in a Tuesday statement that she was “encouraged” by the news of that bump after a call with governors and the Biden administration. The news would provide some relief to Maine providers working to vaccinate as many older people as possible while also continuing to inoculate health care workers. Demand for vaccines has outstripped supply, and many older Mainers are anxiously awaiting an appointment.

The 16 percent increase would raise Maine’s weekly share of doses from 17,575 to 20,375 through mid-February. The additional vaccines would be distributed in line with the state’s current efforts, with a focus on getting vaccines to older Mainers, Mills said.

Detailed figures posted on the Centers for Disease Control and Prevention website Tuesday showed that the government plans to make about 10.1 million first and second doses available next week, up from this week’s allotment of 8.6 million. The figures represent doses of both vaccines. It was not immediately clear how long the surge of doses could be sustained.

The increase comes amid complaints from governors and top health officials about inadequate supplies and the need for earlier and more reliable estimates of how much vaccine is on the way so that they can plan accordingly. Seeking to those concerns, Biden’s team pledged to provide states with firm vaccine allocations three weeks ahead of delivery to allow for accurate planning for injections during their first virus-related call with the nation’s governors Tuesday.

“Until now, we’ve had to guess how much vaccine” is coming each week,” Biden said. “This is unacceptable. Lives are at stake.”

Biden’s announcement came a day after he grew more bullish about exceeding his vaccine pledge to deliver 100 million injections in his first 100 days in office, suggesting that a rate of 1.5 million doses per day could soon be achieved.

The administration has also promised more openness and said it will hold news briefings three times a week, beginning Wednesday, about the outbreak that has killed over 420,000 Americans. 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.

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 afternoon, the CDC reported that just over half of the 44 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.

Story by Jonathan Drew and Zeke Miller. Bangor Daily News writer Caitlin Andrews contributed to this report.