Buoyed by a surge in vaccine shipments, states and cities are rapidly expanding eligibility for COVID-19 shots to teachers, 55-and-over Americans and other groups as the U.S. races to beat back the virus and reopen businesses and schools.

Arizona, Connecticut and Indiana have thrown open the line to the younger age bracket. Pennsylvania and Wisconsin are reserving the first doses of the new one-shot vaccine from Johnson & Johnson for teachers. And in Detroit, factory workers can get vaccinated starting this week, regardless of their age.

Giving the vaccine to teachers and other school staff "will help protect our communities," Pennsylvania Gov. Tom Wolf said. "It's going to take burdens off our parents and families. It's going to make our schools get back to the business of teaching our kids."

Up to now, the vaccination campaign against the outbreak that has killed over a half-million Americans has concentrated mostly on health care workers and senior citizens.

Around the U.S., politicians and school administrators have been pushing hard in recent weeks to reopen classrooms to stop students from falling behind and enable more parents to go back to work instead of supervising their children's education. But teachers have resisted returning without getting vaccinated.

The U.S. has administered nearly 80 million shots in a vaccination drive now hitting its stride, according to the Centers for Disease Control and Prevention. More than 20% of the nation's adults, or close to 52 million people, have received at least one dose, and 10% have been fully inoculated.

President Joe Biden said Tuesday the U.S. expects to have enough vaccine by the end of May for all adults, two months earlier than anticipated, though it is likely to take longer than that to administer those shots. He also pushed states to get at least one shot into the arms of teachers by the end of March and said the government will provide the doses directly through its pharmacy program.

In Wisconsin, teachers will get priority when the state receives its first shipment of about 48,000 doses of the J&J vaccine, health authorities said. Pennsylvania teachers will likewise be first in line when an expected 94,000 doses of the J&J formula arrive this week.

Washington Gov. Jay Inslee announced this week that educators, school staff and child care workers can now get shots.

And in Massachusetts, about 400,000 teachers, child care workers and school staff will be eligible to register for vaccinations starting March 11, Gov. Charlie Baker said Wednesday, though he warned that it could take some time to book appointments because the supply remains limited.

Tennessee will open up vaccinations Monday to an estimated 1 million people over 16 who have high-risk health conditions and those in households with medically fragile children.

The rush to vaccinate comes as many states ease restrictions on people and businesses, despite repeated warnings from health officials that the U.S. is risking another lethal wave. Biden on Wednesday called out the Republican governors of Texas and Mississippi for lifting their mask rules.

"We are on the cusp of being able to fundamentally change the nature of this disease," the president said. "The last thing we need is Neanderthal thinking that in the meantime, everything's fine, take off your mask, forget it. It still matters."

Mississippi Gov. Tate Reeves snapped back on Twitter. "Mississippians don't need handlers. As numbers drop, they can assess their choices and listen to experts," he said. "I guess I just think we should trust Americans, not insult them."

While deaths and newly confirmed infections have plummeted from their peaks in January, they are still running at high levels. The U.S. is averaging close to 2,000 deaths and 66,000 cases per day.

CDC Director Dr. Rochelle Walensky encouraged Americans to "do the right thing" even if states lift their restrictions.

Vaccinations are seen as key to getting people back to work and revitalizing the battered economy.

"The more people we can get the safe and effective vaccine, the faster we can return to a sense of normalcy," Michigan Gov. Gretchen Whitmer said in a statement Wednesday announcing that all people ages 50 to 64 can start getting vaccinations on March 22.

Cindy Estrada, a vice president at the United Auto Workers, said there have been illnesses and deaths among factory workers, so Detroit's decision to offer them shots "is incredibly important."

"It's going to give them some peace of mind," she said as she bared her arm for a shot.

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Associated Press writers Chris Gygiel in Olympia, Washington; David Eggert in Lansing, Michigan; Ed White in Detroit; Scott Bauer in Madison, Wisconsin; Marc Levy in Harrisburg, Pennsylvania; Kimberlee Kruesi in Nashville, Tennessee; and Alex Jaffe, Nancy Benac and Zeke Miller in Washington contributed to this story.