vaccine production and distribution ramp up and more states begin to heed a call from President Biden to expand access to all adults by May.
States are also racing to stay ahead of the growing number of virus variants, some of which are more contagious and possibly even more deadly. At least three states — Maine, Virginia and Wisconsin — and Washington, D.C., have said that they will expand eligibility to their general population by May 1, the deadline that Mr. Biden set last week. At least six other states — including Colorado, Connecticut, Ohio, Michigan, Montana and Utah — hope to do so this month or next.
In Mississippi and Alaska, everyone age 16 or older is eligible, and Arizona and Michigan have made the vaccines available to all adults in some counties.
Mr. Biden said last week that he was directing the federal government to secure an additional 100 million doses of the Johnson & Johnson vaccine. With three vaccines now in use, Mr. Biden has said that the United States will have secured enough doses by the end of May for shots to be available for all adults.
Several states have already been expanding eligibility for vaccinations. In Ohio, vaccines will open to anyone 40 and up as of Friday, and to more residents with certain medical conditions. Indiana extended access to people 45 and older, effective immediately.
Coloradans age 50 and up will be eligible for a shot on Friday, along with anyone 16 years and older with certain medical conditions. Wisconsin said on Tuesday that residents 16 years and up with certain medical conditions would be eligible a week earlier than initially planned.
On Monday, Texans age 50 and older and Georgians over 55 became eligible for vaccines.
In New York State, residents 60 and older are eligible to receive a vaccine, and more frontline workers will become eligible on Wednesday, including government employees, building services workers and employees of nonprofit groups. Gov. Andrew M. Cuomo has yet to announce how or when the state will open eligibility to all adults.
Since vaccinations began in December, the federal government has delivered nearly 143 million vaccine doses to states and territories, and more than 77 percent have been administered, according to Centers for Disease Control and Prevention. The country is averaging about 2.4 million shots a day, compared with well under one million a day in January.
As of Tuesday, 65 percent of the country’s older population had received at least one vaccine dose, according to C.D.C. data, with 37 percent fully vaccinated.
Virus-related cases, deaths and hospitalizations are significantly down from the peak levels reported in January. But progress has slowed noticeably since the start of this month, with continued drops in some states offset by persistent outbreaks in other parts of the country, especially the Northeast.
Public health leaders like Dr. Rochelle Walensky, the C.D.C. director, have warned Americans not to let their guard down prematurely, noting that the amount of new cases remains high, at around 55,000 per day.