Answering growing frustration over vaccine shortages for the coronavirus disease 2019 (Covid-19), President Joe Biden announced that the US is ramping up deliveries to hard-pressed states over the next three weeks and expects to provide enough doses to vaccinate 300 million Americans by the end of the summer or early fall.

Biden, calling the push a “wartime effort,” said Tuesday the administration was working to buy an additional 100 million doses of each of the two approved Covid-19 vaccines. He acknowledged that states in recent weeks have been left guessing how much vaccine they will have from one week to the next.

Shortages have been so severe that some vaccination sites around the US had to cancel tens of thousands of appointments with people seeking their first shot.

“This is unacceptable,” Biden said. “Lives are at stake.”

He promised a roughly 16-percent boost in deliveries to states over the next three weeks.

The administration said it plans to buy another 100 million doses each from drugmakers Pfizer and Moderna to ensure it has enough vaccine for the long term. 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.

The Centers for Disease Control and Prevention reported 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 the Pfizer and Moderna vaccines. It was not immediately clear how long the surge of doses could be sustained.

Governors and top health officials have been increasingly raising the alarm 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.

Biden’s team held its first virus-related call with the nation’s governors on Tuesday and pledged to provide states with firm vaccine allocations three weeks ahead of delivery.

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 more than 425,000 in the United States.

“We appreciate the administration stating that it will provide states with slightly higher allocations for the next few weeks, but we are going to need much more supply,” said Maryland Gov. Larry Hogan, a Republican.