WASHINGTON — President Biden asserted full command of the nation’s vaccination campaignin his prime time address Thursday, framing his first 100 days around a series of new promises that build on the program’s momentum and appear within reach.

Most notably, he directed states and other jurisdictions to make all adults eligible by May 1, setting off a seven-week sprint throughout the country consistent with the accelerating pace of inoculations. Benefiting from manufacturing improvements now boosting the store of doses after months of scarcity, his team has seized the opportunity to mobilize federal resources to rush those doses to Americans promised a semblance of normalcy by July 4.

“If the president is saying it can all get done by May 1, I’m all in,” said Michael Fraser, chief executive of the Association of State and Territorial Health Officers.

The main constraint is still supply, Fraser said, cautioning states against opening the floodgates before taking care of their most vulnerable residents, which is the reason many have hewed to a strict priority system. Those moving quickly to open up eligibility are doing so largely because so many people are hesitant to get the shots, he said, which foreshadows significant hurdles in reaching the level of immunity needed to corral the virus.

Biden seemed to acknowledge as much when he said opening eligibility to all adults by May 1 does not mean everyone will be able to get a shot on that date. Appointments may still prove elusive in some places, given the patchwork nature of the rollout and the gradual increase in supply.

But as with his previous goals, which were achievable because they reflected progress already in motion, this one squares with what’s happening inside factories and on the ground.

Alaska, for instance, became the first state to remove virtually all eligibility requirements, as the governor, Republican Mike Dunleavy, said this week that anyone 16 and over could sign up for a vaccine. Michigan is throwing open appointments to the general public beginning April 5, while Wisconsin health officials announced the state would do so May 1. Other states are also expanding eligibility more gradually: Ohio, Indiana and West Virginia have opened appointments to those 50 and older. The same age cohort will become eligible next week in Texas. In Georgia, availability will expand next week to those 55 and older.

The Biden administration is sticking with May 31 as its target for having enough supply to cover the entire adult population, while stressing that it may take longer to fully immunize everyone who comes forward, especially using the two-dose protocols developed by Pfizer-BioNTech and Moderna. Johnson & Johnson’s vaccine is given as a single shot. Only the Pfizer-BioNTech product has been authorized in the United States for people as young as 16.

The approach of expanding vaccine eligibility before everyone can get inoculated parallels earlier phases of the rollout. Health-care workers gained access to the shots at the program’s outset in December, though many states did not finish immunizing those who were willing until well into the new year.

Biden’s strategy is not without risks, from manufacturing setbacks and logistical breakdowns as states seek to scale their programs to the rapid spread of new and more transmissible variants of the virus that could sicken people before they get vaccinated.

But he paired the updated timeline with a suite of initiatives aimed at expanding the number of vaccinators and the places where people can get shots, buttressing existing federal support for what his aides have repeatedly described as a “wartime effort.”

WEBSITE TO DEBUT

The president unveiled plans for a federally supported website, also slated to go up by May 1, to help people find vaccine appointments. Details were sparse, and it was not immediately clear how such a website might sync with a jumble of state and commercial platforms. Such plans carry risks given frustrations with some existing sites, as well as the failure of HealthCare.gov, which crashed within two hours of its launch in October 2013. Jeff Zients, the coordinator of the White House’s coronavirus task force, was tapped at the time to salvage the website.

Trump last year also touted a website that he claimed would help Americans find coronavirus tests, purportedly set up by Google, that fell far short of his promise.

In this case, Biden’s plan builds on technology created during a previous pandemic. In late February, the Centers for Disease Control and Prevention partnered with Boston Children’s Hospital to launch VaccineFinder.org, which allows users to search nationwide for vaccine providers. By entering their Zip codes, users receive a list of nearby providers with contact information and links to eligibility criteria, as well as information about whether the providers have doses available.

The VaccineFinder site was started by Google during the H1N1 influenza outbreak in 2009 and subsequently taken over by John Brownstein, chief innovation officer at Boston Children’s, to help with distribution of flu and other routine vaccines, such as shingles and hepatitis.

The site has limitations that Brownstein said he hopes to address in coming weeks, including the way it directs users to others’ website, rather than allowing them to schedule appointments directly. Also, it does not currently send out follow-up reminders for the second shots that are part of the Pfizer-BioNTech and Moderna regimens.

“Our hope is, with all the fragmented and siloed systems, to provide the nation with resources to help support consumers,” Brownstein said. “We have plans to include appointment availability and other functionality that will make that even easier.”

Zients said Thursday the website would be paired with a call center geared toward those without access to the internet. He also said the administration would deploy “technology teams” to help improve state and local systems to schedule vaccine appointments.

Officials expect that signing up for vaccine appointments will become simpler once there are more slots to go around. But more slots also require more staff and more space.

MORE TO ADMINISTER VACCINES

The administration is making dentists, paramedics and midwives, among others, eligible to administer vaccine, building on state initiatives to surge the workforce. An additional 4,000 active duty troops will support vaccination efforts, bringing the total military deployment to more than 6,000, the White House said.

Shots will soon be available at many more locations: The administration plans to double the number of pharmacies offering vaccine, bringing the total to more than 20,000, and to direct more supply to community health centers, involving nearly 1,000 such sites throughout the country. The number of mass vaccination centers supported by the Federal Emergency Management Agency will also double, according to senior administration officials. Currently the federal government has opened or plans to open 21 such centers, in states ranging from California to Florida.The latest addition is a site at Detroit’s Ford Field.

“The Biden administration is paying close attention to the steps that are necessary to get the vaccine from a vaccine depot into the arms of members of the public,” said John Auerbach, president and chief executive of Trust for America’s Health and a former Massachusetts public health commissioner.

State and local health officials say vaccine supply is still the main factor limiting how many inoculations they can perform. Supply is expected to remain tightly constrained through much of March but then expand considerably in April. States have been advised to plan for nearly 25 million doses a week by the beginning of next month.

Meanwhile, the nation is now averaging more than 2 million shots a day, and about 65 percent of adults 65 and older have received at least one dose. Biden said Thursday his original vow of 100 shots in his first 100 days, which experts panned in January as not nearly ambitious enough, would be cleared within 60 days.

The accelerating pace of inoculations has not prompted every state to expand eligibility rapidly, however. New Mexico has kept shots targeted at its most vulnerable residents even as it achieves among the fastest rates of vaccine administration. Other states that have quickly made use of doses include North Dakota, Wisconsin and Massachusetts.

“Each week in February and March, we have seen our vaccine grow, and even more vaccine is anticipated as we move into April and May,” Julie Willems Van Dijk, Wisconsin’s deputy health secretary, said in a Thursday briefing, explaining why everyone 16 and over would become eligible in May.

She said 80 percent of the state could be vaccinated by June, but that hesitancy about the shots may lead as much as 40 or 50 percent of the population to pass on immunization – a significant hurdle for health officials, beyond supply of shots and the capacity to administer them.