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More California counties are opening up vaccines to younger adults, a week ahead of the state broadening eligibility to everyone 16 and up.

At the same time, California public health officials warned Thursday of decreases in supply because of a national reduction of the one-shot Johnson & Johnson vaccine in coming weeks.

The state has received about 2.4 million doses this week, but it expects 2 million next week and 1.9 million doses the week after. This is in addition to vaccine shipped directly to pharmacies and community health centers from the federal government.

Santa Clara County in the San Francisco Bay Area and Fresno County in the central valley are the latest to open up vaccinations to everyone eligible to get one. People age 16 and up can get the Pfizer vaccine while the Moderna and Johnson & Johnson vaccines are for people 18 and older.

“The supply of COVID-19 vaccine has become more stable. We are able to move ahead of the (state) timeline and have been approved to lift the current restrictions in place to expand eligibility,” said Joe Prado, who is heading up Fresno County’s vaccinations.

That might not be the case next week when eligibility expands statewide and vaccine supply shrinks.

But this week, availability remains mixed, with some places reporting an excess of open appointments. Humboldt County in northern California, for example, urged residents to make an appointment, saying that “hundreds of doses” were available through the weekend.

Similarly, a mass vaccination site at California State University, Los Angeles announced it would take adults on a walk-up basis because of excess appointments. But by late Thursday morning, the site was turning people away because of demand.

California Office of Emergency Services spokesman Brian Ferguson said in an email to The Associated Press on Thursday that advance registration through the state’s My Turn system is the only way to guarantee a vaccination there.

“To the extent to which those appointments go unfilled, there may be a limited number of appointments available as walk ups for individuals 18+ between tomorrow and continuing through Sunday when management of the site transfers to the city,” he said.

Gov. Gavin Newsom announced Tuesday that the state of nearly 40 million will lift most pandemic restrictions June 15 provided hospitalization rates stay low and there is enough vaccine for everyone. It’s unclear if the drop in supply will affect California’s reopening date, although the governor’s office said on social media that “CA is on track to open safely 6/15.”

California has already vaccinated 72% of seniors 65 and older with at least 1 dose, and 43% of the population 16 and older has received at least 1 dose. More than 8 million people of an estimated 32 million eligible are fully vaccinated.

Californians 16 and older can make appointments starting April 15.