Public health officials are concerned the supply drop could impact the state's plans to reopen the economy in June.
"We really thought we'd be swimming in vaccine by mid-April," said Desi Kotis, Chief Pharmacy Executive for UCSF Health. "That's clearly not the case."
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California currently has around five million doses for the next two weeks. But, the incoming supply is shrinking.
The state reports its supply will be cut by 15 percent next week - dropping from 2.4 million doses to 2 million doses. Another 5 percent drop is projected the following week.
"It's disappointing," Kotis said. "We've been told for many months now by mid-April you will have as much vaccine as you need."
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According to data released by the state, California received more than 574,000 doses of Johnson and Johnson vaccine this week. Next week, the state is only receiving 12 percent of that allotment. The following week it dips down further to only 4 percent.
Kotis explains UCSF partnered city-run vaccination sites like San Francisco City College have the capacity to administer 5,000 to 7,000 shots per day. But, they've been consistently waiting for supply increases in order to meet that goal.
Next week is no different.
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"We are receiving about what we received last week," Kotis said. "We still have some second doses and we'll know more probably on Sunday."
The drop in doses is coming at a critical time. Next Thursday, the state is expanding vaccine eligibility to all Californians 16 and older.
There are roughly 18 million people living in the state that have yet to receive a shot, according to estimates from 2020 census data. But, the state's current supply is around five million doses.
"The more people that we get vaccinated, the quicker we can turn the page and end this pandemic," Gov. Gavin Newsom said Thursday in Fresno County.
But, experts question whether supply will be able to meet the demand in time for the economy to safely reopen by June. Kotis expects we should have that answer by May.
"Hopefully by the beginning of May, at least for Pfizer and Moderna, we'll have larger quantities coming into California," Kotis said. "I want to stay cautiously optimistic."
Currently, 54 percent of San Franciscans over 16 have received at least one dose. Kotis says herd immunity levels won't be met until that number is at or above 85 percent.
VACCINE TRACKER: How California is doing, when you can get a coronavirus vaccine
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