Governments and health districts in Virginia, Maryland and the District are preparing for about 1 million more young people to become eligible for a coronavirus vaccine as early as next week, when federal officials are expected to authorize the two-dose Pfizer regimen for 12-to-15-year-olds.

Officials say the flood of newly eligible people will help use up existing supply and boost immunity as demand for the vaccine starts to ebb among the adult population. They are exploring a range of options for inoculating younger teens, including the mass vaccination sites and clinics where shots are administered to adults, targeted clinics in schools and pediatricians’ offices.

Once the Food and Drug Administration authorizes the Pfizer-BioNTech coronavirus vaccine for 12-to-15-year-olds, the Centers for Disease Control and Prevention must adopt a federal advisory committee’s recommendation before vaccinations can begin. Canada authorized the use of the Pfizer vaccine for that age group on Wednesday.

Virginia Gov. Ralph Northam (D), a pediatric neurologist, said federal authorization would add about 400,000 to 500,000 eligible people in Virginia. His office said the state’s supply of doses is robust enough to absorb the extra demand, and health officials are working with local health districts and school systems to make it happen.

Northam said Virginians appear eager to get young people vaccinated, citing a survey by Virginia Commonwealth University that found that 66 percent of parents plan to get their adolescents vaccinated and 63 percent said they would get younger children vaccinated. He also said he anticipates the federal government authorizing vaccines for infants as young as 6 months old by September.

In Maryland, the 455,000 young people who would become eligible could receive the shots anywhere the Pfizer vaccine is offered, including local health departments, pharmacies and mass vaccination sites, Health Department spokesman Charles Gischlar said. Pediatricians’ offices will also have doses, he said.

“There is no current mandate to get vaccinated but we encourage everyone who is eligible to do so to protect themselves, their families and their community,” Gischlar said in an email.

Dan Finkelstein, a pediatrician with the 25,000-patient Capitol Medical Group in Chevy Chase, said his practice is considering offering coronavirus vaccinations by appointment in its parking lot. They would probably follow a model used for the flu vaccine last fall, in which nurses administered 500 doses every Saturday and Sunday for 12 consecutive weekends. But they would do it on weekdays, and add time to observe patients for possible side effects.

Finkelstein said the state only reached out this week to ask if the practice wanted to administer the vaccine; doctors were given no indication of how many doses they would receive and when.

Parents have expressed “huge interest” in getting their children inoculated, and pediatricians recommend it, Finkelstein said, even though children are not at high risk of developing severe cases of covid-19. “The biggest concern to us as pediatricians is if they get it and convey it to parents or grandparents,” he said.

Northam also said Thursday that he expects to lift most remaining limits on gatherings and mandates for social distancing on June 15 if positive trends in coronavirus infection and vaccination rates continue. But masking requirements would remain in place at least until the end of June, he said, and potentially longer if federal guidelines suggest it.

The seven-day average of new daily coronavirus cases fell to 9.49 per 100,000 residents in the District on Thursday, according to The Washington Post tracker, the first time it was below 10 since Oct. 28. Maryland’s seven-day average fell to 11.36 per 100,000 residents, the lowest number since Oct. 26. Virginia’s seven-day average has declined to 10.13 new daily cases per 100,000 residents, the fewest since Oct. 7.

David Gaskins, 51, of Ashburn, said his 15-year-old daughter is already registered to receive the vaccine at Dulles Town Center, in part because his mother and father will be visiting from Texas soon.

Gaskins, his wife, their 18-year-old daughter and his parents are all fully vaccinated, and they have carefully followed public health guidelines throughout the pandemic. When the family heard adolescents would soon be eligible, his daughter asked him, “What should I do?” Gaskins said.

He said he advised her, “If we think it’s coming, let’s go ahead and get in front of the line.”

Roberta DeBiasi, chief of pediatric infectious diseases at Children’s National Hospital in the District, said the hospital began registering children ages 12 to 15 on Wednesday. By Thursday afternoon, about 3,500 were on the list.

Natalie Talis, population health manager at the Alexandria Health Department, said officials are working with schools to provide vaccinations on-site and coordinate field trips to existing sites.

More importantly, she said, the city is helping prepare teachers, school nurses, recreation center staff and doctors to answer parents’ questions.

“There’s a big difference between making the decision for yourself to get yourself vaccinated and helping to make that informed decision about your family member,” she said. “We’re hoping to hit the ground running whenever we get the full okay.”

Arlington health district spokeswoman Jessica Baxter said officials will share more information about their rollout plan after the federal authorization is finalized.

Alison Ansher, director of the Prince William County’s health district, said families will be able to get the shot through a pediatrician or family doctor, at one of the county’s mass vaccination sites or at a pharmacy. School sites may be added later as well.

“We have over 30,000 in the public schools alone,” Ansher said, regarding the number of youngsters who would be eligible.

Ansher said schools will initially help spread the word about vaccine eligibility and transport young people to vaccination sites.

Babur Lateef, chairman of Prince William’s school board, says the school system will have a vaccination program, but the details have yet to be determined. “We are working on the logistics to start vaccinating those kids,” Lateef said. “We hope to start vaccinating the minute feds approve it for that age group.”

Schneider reported from Richmond. Ovetta Wiggins and Julie Zauzmer contributed to this report.