SANTA CLARA COUNTY, Calif. (KRON) – The California Department of Public Health confirmed that there are 11 cases of a new omicron sub-variant in California, with at least two cases in Santa Clara County.

The BA.2 subvariant has been dubbed “stealth omicron,” a variant inside the variant.

The omicron variant is made up of three main substrains, BAs 1-3, and until Dec. 23 the World Health Organization said 99% of cases sequenced were BA. 1, Fortune reports.

Modeling by Dr. JP Weiland shows BA. 2 cases grew 90-120% faster than BA. 1, based on Danish numbers. Weiland says data doesn’t yet confirm whether increased spread is because of higher transmissibility or increased immune escape by BA. 2.

Some experts say BA. 2 also shows possibilities of reinfection in people who only recently had BA. 1 omicron.

In addition to its speed, BA. 2 doesn’t have a mutation that BA. 1 had – a deletion in the spike gene – which made that strain easier to identify as omicron on PCR tests. Despite some rumors, this doesn’t mean it can’t be detected, however.

Should we be worried?

Danish officials say not just yet – especially given hospitalization numbers.

“Initial analysis shows no differences in hospitalizations for BA.2 compared to BA.1,” Denmark’s Statens Serum Institut said in a statement. “It is expected that vaccines also have an effect against severe illness upon BA.2 infection.”

But Dr. Eric Feigl-Ding, Federation of American Scientists epidemiologist, says swift action to quell transmission in the U.S. is needed – especially given early signs it could cause re-infection in those who’ve just recovered from BA. 1, which he calls “vanilla omicron.”

Despite quick spread, many experts say it’s still too early to know if BA.2 will cause more severe illness than omicron.

Nexstar Media Wire contributed to this report.