SANTA ANA, Calif. (AP) — California will start vaccinating anyone 16 and over against the coronavirus starting in three weeks, expanding eligibility to the shots along with a host of other states as a long-awaited boost in vaccine supplies is in sight.

Gov. Gavin Newsom announced Thursday that the nation's most populous state would start vaccinating anyone 50 and over in a week and the population more broadly — except those under 16, for whom vaccines have not yet been authorized — on April 15.

The decision comes as California, which was initially slow to roll out the vaccines but has ramped up inoculations in recent weeks, expects to receive 2.5 million doses a week in the first half of the month and more than 3 million a week in the second, a big jump from the roughly 1.8 million doses a week currently.

“In just a few weeks, there’ll be no rules, no limitations, as it relates to the ability to get a vaccine administered," Newsom said at a news conference in Orange County. “This state is going to come roaring back."

The move comes as some California counties have veered away from the state’s eligibility criteria by opening up the shots for people with a broader range of medical conditions than those required in most places, and in some cases, at younger ages. It also comes as governors across the country have expanded eligibility for the vaccine as supplies have increased. Earlier this month, Alaska opened eligibility to any resident over 16. Florida said Thursday it will open eligibility to anyone 18 and over on April 5, while Texas will start inoculating all adults next week.

President Joe Biden’s administration wants all states to make every adult eligible for the vaccine by May 1.

Even with the expansion, it will take several months for willing Californians to be vaccinated, state officials said.

Some county officials were eager to vaccinate more people while others said they were concerned there wouldn't be enough doses to keep up with rising demand. In Southern California's Riverside County, more appointments have been available recently due to the boost in vaccine supplies. The county opened up 30,000 appointments this week, far more than previously weeks when slots hovered in the low 20,000s, said Jose Arballo, a spokesman for the county's health agency.

“Any time we can vaccinate more people, that’s a good thing,” Arballo said. “We believe we’ll have the supply needed to handle any increase in eligibility.”

But while Kern County health officials welcomed the expansion, they also urged residents who qualify now to sign up for their shots "as we are unsure what the availability of vaccination appointments will look like once these additional eligibility groups are opened.” Santa Clara County Health Officer Dr. Marty Fenstersheib said his county has been told it will get 58,000 doses next week, but the state will begin allowing about 400,000 more people between the ages of 50 and 64 in the county to sign up, in addition to the current backlog.

“That 58,000 doses doesn’t go very far. We have the capacity to administer over 200,000 doses,” he said. “We don’t have the vaccine and we are concerned, beginning next week when we add that additional 400,000.”

California so far has administered more than 15 million doses of the coronavirus vaccine. Initially, more affluent residents who could afford to spend hours scouring complicated web portals were snagging more appointment slots, prompting public health officials to take measures aimed at getting more of the doses to underserved communities where the virus has hit the hardest.

In recent weeks, the state of 40 million people has seen coronavirus infections plummet following a winter surge. That has paved the way for more businesses to reopen and more schools to bring back in-person instruction, and state public health officials have said more activity can resume as vaccinations continue to rise in the poorest communities.

Newsom said Thursday the state will continue to target underserved communities by working with labor groups to reach essential workers and letting health providers target vaccinations by ZIP code.

Since California opened eligibility earlier this month to people with developmental disabilities and those with serious health conditions such as cancer, some residents said they've seen people without those conditions get in line for a shot, too, knowing that vaccination sites are operating on an “honor system” and won't require medical documentation.

Dr. Louise Aronson, a leading geriatrician at University of California, San Francisco and member of the governor’s vaccine drafting guidelines committee, said in a recent interview that she knows of too many people who have received the vaccine who don’t qualify. She said she has heard of people claiming eligible occupations at pharmacies that don’t verify and of a worker at a vaccination site in the East San Francisco Bay Area holding back doses for friends.

Part of the problem has been the lack of uniformity between counties, which makes people believe the standards are arbitrary, she said. Some counties have already allowed residents 50 and up to get shots while San Diego County has expanded the range of qualifying conditions to include moderate to severe asthma and being overweight.

“There are a whole lot of cheaters, and this is just my anecdotal experience,” Aronson said.

Eyal Oren, associate professor of epidemiology at San Diego State University, said there have been many changes in the vaccination system as supplies have increased and he believes the doses are finally there to expand eligibility.

“We’re in this race of trying to get more people immunity,” he said.

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Associated Press writers Janie Har, Juliet Williams and Jocelyn Gecker in San Francisco contributed to this report.