They line up by the hundreds each hour, dutifully masked and spaced 6 feet apart along the vast corridors of the Hynes Convention Center — a vaccination site supersized by the Federal Emergency Management Agency.

This is the White House vaccine push at work in Boston. Residents eager for a shot and a return to normalcy, are ushered into a post-pandemic world by hundreds of Navy sailors in face shields and camouflaged uniforms. They plug away with needles, smiles, and factory-like precision at scores of stations in the site’s cavernous “Vaccination Hall.”

“It’s nice,” said Navy Seaman Triniti Tolbert, a 19-year-old corpsman dispatched to Boston this month from her base in Virginia, injecting a new arrival every three to six minutes. “I want everyone to be outside again enjoying their lives.”

The federal government is rapidly expanding its role in immunizing residents in Massachusetts and beyond against COVID-19, setting up mega-vaccination sites around the country and increasingly shaping state policies about how vaccines are distributed.

This week’s recommendation by US health officials to suspend the use of Johnson & Johnson’s vaccine, forcing state leaders to quickly fall in line, was the latest example of Washington taking the lead in a vaccination program that, before the inauguration of President Biden, was run largely by the nation’s governors. The move created a swirl of confusion, but federal officials insisted it won’t disrupt the broader inoculation drive.

Where former President Trump was content to leave most vaccine decisions to states, the Biden administration has taken a more activist posture, insisting, for example, that everyone should be eligible for a shot by April 19. The federal government also is leaning on Massachusetts and other states to get more doses to hard-hit communities and open appointments more quickly to more people, ranging from teachers to those with chronic health conditions.

At the Hynes alone, FEMA has deployed 215 sailors to work as vaccinators and is adding 6,000 doses a day to the 1,000 sent from the state’s allocation. Overall, nearly a third of all doses arriving in Massachusetts last week were channeled directly from the federal government to retail pharmacies, community health centers, and military and veteran facilities.

“There’s been a dramatic change over the past month, and much of it has to do with the additional [federal] resources going into these communities,” said Senator Edward Markey, who pressed FEMA to include Boston among the three dozen mass vaccination sites the agency has set up nationwide.

The ramp-up is set to continue accelerating past April 19, at least through the end of May, when Biden has pledged to make enough doses available to inoculate every American.

“They’re opening the spigot,” said Michael Curry, president of the Massachusetts League of Community Health Centers, whose members are receiving a flood of vaccine doses directly from the federal government. The centers, which serve many people of color in communities hardest hit by COVID-19, got nearly three times as many federal doses last week as doses from the state allotment.

Federal officials said Tuesday’s pause in administering J&J doses, while health officials examine a rare blood-clotting disorder seen in six of the nearly 7 million recipients, won’t slow down vaccinations because they’ve purchased so many doses from two other vaccine makers. But the decision — made by US health officials, not the White House — complicates the rollout, forcing vaccination sites in the states to reschedule hundreds of thousands of appointments nationwide.

Even so, direct federal supplies have been increasing at a faster clip than the federal doses allocated to the state government, which has anchored the four-month vaccination program.

Retail pharmacies are the largest recipients of federal doses. More than 250,000 were sent directly to hundreds of pharmacy outlets in Massachusetts last week, a 67 percent jump from the prior week. In addition to 120 stores that already ran injection centers, CVS opened 220 others in the state last week just to handle a one-time surge of J&J vaccines.

“We fill these vaccine bookings in Massachusetts pretty quickly,” Dylan Rybka, the Wellesley-based regional vaccine leader for CVS Health, said on a tour of a pharmacy injection site in Cambridge’s Porter Square last week.

CVS and other vaccine providers have now stopped giving out J&J vaccines and are scrambling to reschedule bookings.

The number of federal doses sent to more than 30 of the state’s community health centers climbed 51 percent last week to 88,400. By contrast, the Baker administration’s vaccine allocation rose 16 percent to 444,930 doses.

Officials with the White House COVID-19 Response Team insist they aren’t in competition with the states. They say they’re working in tandem with state leaders to stress vaccine speed and access and fill gaps when they see them, calling it a “whole of government” or “all of the above” strategy.

“It’s really important that we bring vaccine where people are,” White House virus response coordinator Jeffrey Zients said in a press briefing last week.

Nationally, vaccination sites of all types averaged more than 3 million shots a day last week, including a record 4.6 million on Saturday. More than 72 million Americans — over one in four adults — have been fully vaccinated. But the Biden administration is hoping to pick up the pace to slow the spread of highly contagious COVID-19 variants that are increasing infections nationally even as more people gain immunity.

Independent analysts say federal officials seem to be using their own supply channels partly as a way to prod states to align themselves with White House vaccination goals.

“You’re seeing the Biden administration working on a practical level to set national benchmarks for when and how things should be done,” said David E. Williams, president of the Boston consulting firm Health Business Group. “They’re using the supplemental doses to enforce federal priorities and influence what’s happening on the ground in the states.”

That dynamic unfolded in Massachusetts on March 2 when Biden called on states to prioritize teachers for vaccinations to hasten the reopening of schools. The state’s CVS stores that were part of the federal retail pharmacy program began booking vaccine appointments for teachers immediately even though educators weren’t yet eligible under the state timetable.

The next day, Governor Charlie Baker bowed to the federal directive and added teachers to the eligibility pool.

Federal officials also have been using their own program to press for greater equity, a Biden goal to get vaccines to Black, Hispanic, and immigrant populations that’s shared by Massachusetts officials but neglected elsewhere.

In Florida, for example, the Biden team has created mass vaccination sites to serve marginalized residents in Miami, Jacksonville, Tampa, and Orlando. Only a small fraction of the doses allotted to Florida officials had gone to those residents; instead, the state channeled more to upscale communities.

“They’re trying to address gaps they see and influence state policies,” said Jen Kates, a senior vice president and global health policy director at the Kaiser Family Foundation. “The states don’t have to follow their lead, but a strong suggestion from the federal government does make a difference.”

While its hand is increasingly visible, the Biden administration has in some cases embraced practices already in effect in states. Federal officials in March significantly raised Medicare payments to providers of COVID-19 vaccines to almost the same rate Massachusetts had set in January. And when the president last week moved up the eligibility date for all adults to April 19, he chose the same date — Patriots Day in Massachusetts — that Baker established weeks earlier.

“It was terrific that he followed our lead,” Baker told reporters, deadpan, at a press briefing in Boston last week.

Amid the J&J uncertainties, White House officials are relying more heavily now on two-dose vaccines from Pfizer-BioNTech and Cambridge-based Moderna. Those companies are on track to deliver a total of 400 million doses by the end of May.

The mass vaccination site at the Hynes, which is using the Pfizer-BioNTech vaccine, is a unique model of a jointly run state and federal program. While the bulk of the doses are supplied by FEMA, the site is being operated by a state contractor, CIC Health, which trained the Navy medical personnel.

“We’re vaccinating about 700 people an hour,” said Rodrigo Martinez, a logistics expert who holds the title of chief experience officer for CIC Health. “We want the people to have the best health care experience they ever had here.”

Martinez said the operation is expanding this week to include mobile units that will ferry vaccine from the Hynes every morning to “pop-up” sites in Boston neighborhoods and nearby communities such as Chelsea and Revere, which have been ravaged by the coronavirus.

At the Hynes last week, each person vaccinated had a different story, but all shared the goal of resuming life without COVID-19 worries. For coffee shop manager Fatiha Mazza, the jab in the arm would mean a long-delayed chance “to travel, to see my parents in Morocco” later in the year.

Navy Commander James Bach, who was supervising the vaccinators, said it was a gratifying mission.

“Everybody on my team is working 12 to 15 hours a day, and there’s no complaints,” he said. “There’s a real sense of purpose. They’ll stay till the last shot.”