California experienced a massive burst of allergic reactions after administering the coronavirus vaccine to its residents, forcing state leaders to suspend the inoculation of its population amid its already struggling vaccine rollout.

The state stopped administering hundreds of thousands of doses after one batch of its Moderna COVID-19 vaccines was apparently linked to a severe allergic reaction that affected six health care workers. The individuals received their vaccine doses at the Petco Park mass vaccination site last week in San Diego.

Vaccine Side Effect?

On Sunday, the California Department of Public Health released a statement urging health care providers to stop administering the coronavirus vaccine that came from the same batch that previously arrived between January 5 and January 12.

Officials distributed the batch that included more than 330,000 doses to 287 health care providers across California. The doses were set to expire by July but will not be thrown out. They will be used in the investigation when public health and Moderna officials discover more information about the incident.

“It’s probably prudent to hold them, but every time a vaccine isn’t given out, it’s slowing us down,” infectious disease physician at UCSF, Dr. Monica Gandhi, said.

Across California, about 43% of its 3.2 million coronavirus vaccine dose supply has been distributed to local health departments and providers as of Sunday.

While some vaccines from Moderna have already been administered to residents, authorities are unsure of exactly how many and where they have been given. On Sunday, state officials noted that other areas that used doses from the same batch did not record similar allergic reactions among its recipients.

However, on Monday, two vaccination clinics canceled appointments due to not being able to guarantee vaccine doses after the issue with Moderna’s batch. Health care providers in San Francisco, Alameda, and Santa Clara counties all received vaccine doses from the same batch. Officials from those regions announced that the distribution of the treatment has come to a halt after the incident.

The San Francisco Department of Public Health has not yet canceled its vaccination appointments and is trying to finish what has already been scheduled. The agency still has about 8,000 doses of the Moderna vaccine from the same batch.

Setback of Treatment

“This setback comes at a time when vaccine is scarce and when SFDPH allocation from the state arriving this week is only 1,775. This will have an impact on the overall city’s ability to complete scheduled appointments,” a spokeswoman for the department said.

The six people that developed the severe allergic reaction reported symptoms within 24 hours of each other. “That number, clustered together, was slightly higher than expected for the time period,” San Diego County’s director of epidemiology, Dr. Eric McDonald, said. The medical professional noted that authorities swapped the batch to avoid the potential connection between the two.

Regulators of the vaccine recommend officials to observe individuals who have received doses of the treatment for about 30 minutes afterwards to see if they develop any side effects. This process was made after a small number of people experienced severe allergic reactions after being inoculated, the San Francisco Chronicle reported.

On Monday, Moderna said it was working with the state health department to investigate the reported allergic reactions. The pharmaceutical company said it was not aware of similar side effects from other vaccination sites that used doses from the same batch of vaccines.

“Moderna acknowledges receiving a report from the California Department of Public Health that a number of individuals at one vaccination center were treated for possible allergic reactions after vaccination from one lot of Moderna’s COVID-19 vaccine. The company is fully cooperating with CDPH in investigating these reported adverse events,” said a Moderna spokeswoman’s statement on Monday.