An estimated 4,300 people received less of the Pfizer vaccine than they should have, KTVU reported March 4.
Too little of the vaccine was administered due to a problem with syringes on March 1, the media outlet said.
But California health officials said that people received a sufficient dose, and didn't require booster shots.
An estimated 4,300 people were administered less than the recommended dose while getting a shot at the Oakland Coliseum, two unnamed medical workers told the media outlet.
The optimal vaccine dosage is 0.3 milliliters of Pfizer, but thousands of people received around 0.2 milliliters, KTVU said.
Due to a problem with the syringes, too little of the COVID-19 vaccine was administered, the media outlet reported.
The mix-up took place in the morning but was identified and resolved by 2 p.m., state officials told KTVU.
Both agencies that run the mass-vaccination site - the California Governor's Office of Emergency Services and the Federal Emergency Management Agency - were unaware of the issue until KTVU alerted them of it on March 2.
Cal OES, the Federal Emergency Management Agency, the State Department of Public Health, the United States Department of Health and Human Services, and Pfizer held emergency meetings on March 2 to discuss the error, a Cal OES spokesperson told the media outlet.
Cal OES did not deny that a lesser dose had been given. Instead, a spokesperson told KTVU that the amount not given to people was "negligible." Therefore, nobody had been called back for an extra booster shot, he said.
Cal OES told KTVU that Pfizer had told the agency that there's no reason to be concerned, unless someone were to receive less than half of a single shot - in which case they should get another shot right away.
In a KRON4 report, officials said the public should be "rest assured that vaccines administered at the Coliseum are being dispensed in a manner consistent with medical and scientific best practices and will work as designed."
Dr. John Swartzberg, the clinical professor emeritus of infectious diseases and vaccinology at UC Berkeley, told KTVU Saturday that people "should be fine" as long as they get their second dose of the vaccine.
The California Department of Public Health has neither confirmed nor denied the allegations provided to KTVU earlier in the week, KTVU reported Sunday.
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