Officials said that a COVID-19 outbreak reported to be among the initial omicron variant cases in the East Bay was connected to a wedding in Wisconsin.

Eleven of the 12 confirmed virus cases logged by Alameda County were Kaiser Permanente’s Oakland Medical Center staff members. All eleven have attended the wedding, as San Francisco Chronicle first reported.

Last Nov. 30, the first case involving a staff member at the Oakland Medical Center was reported. Alameda County confirmed 12 positive cases later that week, noting that most of the cases were believed to be COVID-19 omicron variant, Kaiser Permanente said in a statement.

Alameda County’s health officer Dr. Nicholas Moss, in an interview with the Chronicle, said that at least half of the reported cases were positive for the new virus variant.

The Alameda County Public Health Department and the city of Berkeley released a statement saying that all 12 positive cases, with ages ranging from 18 to 49, have received complete COVID-19 vaccine. Kaiser’s 11 staff members, meanwhile, have already been vaccinated with booster shots.

Eleven of the confirmed cases were from Oakland while one is from Berkeley.

In a statement to SFGATE, Kaiser said that 16 other persons were probably exposed to the virus. Eight of them were employees while the other half were patients. Thirteen have tested negative so far.

The Alameda County and Berkeley health officials said all of the infected persons are placed in home quarantine and only manifest mild symptoms.

Alameda County, the City of Berkeley, and the California Department of Public Health are investigating the cases.