(TNS) — California's second shipment of coronavirus vaccines, set to be delivered next week, will contain far fewer doses than initially expected, Gov. Gavin Newsom's office said Thursday.

Newsom estimated earlier this week that the state would receive an additional approximately 393,900 doses of the Pfizer-BioNTech vaccine in the shipment. It will now receive 233,000 doses — a decrease of 40 percent.

California is one of several states notified by federal authorities since Wednesday that their vaccine shipments would be reduced. The shortfalls led to mass confusion as states prepared distribution plans.

"The numbers we provided for future shipments were projected estimates based on what the federal government had communicated to us," Erin Mellon, a spokesperson for Newsom, said in a statement. "The federal government delayed the number of Pfizer vaccines that California will receive in the next shipment." The state received its first shipment of 327,000 doses of the vaccine this week, and several counties started vaccinating thousands of health care workers in recent days.

It's unclear why federal officials have apparently delayed shipments. Pfizer said it "is not having any production issues" and that none of its shipments has been delayed.

"We have millions more doses sitting in our warehouse but, as of now, we have not received any shipment instructions for additional doses," the pharmaceutical company said in a statement.

The White House did not immediately respond to a request for comment.

A spokesperson for the U.S. Department of Health and Human Services said vaccine allotments for states have not been reduced and that "reports that jurisdictions' allocations are being reduced are incorrect."

"As was done with the initial shipments of Pfizer vaccine, jurisdictions will receive vaccine at different sites over several days," the agency said in an email. "This eases the burden on the jurisdictions and spreads the workload across multiple days."

California had expected to receive about 2.1 million doses by the end of the month. The reduction in Pfizer vaccines, about 160,900 doses, could delay how quickly the state is able to vaccinate health care workers and other essential employees.

The state's first several shipments will go to the estimated 2.4 million health care workers and residents of long-term care facilities in the state. Every person must receive two injections of the Pfizer vaccine, three weeks apart, for it to be effective.

California is still determining who will be inoculated after that first group. Newsom has said teachers and farm and grocery workers could be next in line.

"We are focused on quickly distributing the vaccines we have to Californians in a way that is equitable and transparent," Mellon said.

San Francisco expected to receive five boxes of the Pfizer vaccine in the next shipment, but has been told by state that it will get only three boxes, according to the city's COVID Command Center. Each box has 975 doses.

Contra Costa Health Services has been notified that a shipment of 7,800 doses of Pfizer vaccine expected next week has been reduced to 4,875 doses.

Earlier Thursday, Health and Human Services Secretary Alex Azar told CNBC that he wanted more transparency around Pfizer's manufacturing process, saying the company had kept the federal government at "arm's length."

Pfizer said it has "continuously shared" information with Operation Warp Speed, the administration's program to accelerate vaccine distribution, including details about "every aspect of our production and distribution capabilities."

Washington Gov. Jay Inslee, whose state also lost 40 percent of its vaccine allotment, tweeted that "no explanation was given" by federal authorities.

"This is disruptive and frustrating," he said. "We need accurate, predictable numbers to plan and ensure on-the-ground success."

California's shortfall may be eased in part by the impending arrival of a second vaccine, made by Moderna.

A panel of scientists on Thursday recommended that the U.S. Food and Drug Administration authorize the Moderna vaccine, clearing the way for tens of thousands of additional doses to ship nationwide, including to the Bay Area, as early as next week.

Newsom has said California expects to receive about 672,000 doses from Moderna by the end of the month, if it receives approval.

The panel voted Thursday to recommend the FDA grant emergency use authorization for the Moderna vaccine for people 18 years and older. The FDA will probably do so by Friday, as the agency typically follows the panel's recommendations.

The Moderna vaccine is similar to the vaccine made by Pfizer and BioNTech. Both use a new vaccine technology, called messenger RNA, or mRNA, that injects modified, synthesized genetic material that instructs the human body to produce the "spike" protein of the coronavirus on its own, which then prompts an immune defense.

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