At least 15 states have detected the omicron coronavirus variant and that number is expected to rise, Centers for Disease Control and Prevention Director Dr. Rochelle Walensky told ABC News on Sunday.

“We know we have several dozen cases and we’re following them closely. And we are every day hearing about more and more probable cases so that number is likely to rise,” Walensky said on “This Week.”

The variant, first discovered in South Africa, has several mutations to the spike protein that allows the virus to enter the body, and some of those mutations could lead to increased antibody resistance and transmissibility. Scientists are still collecting data on the virus and the effectiveness of current Covid-19 vaccines.

After being detected in several other countries, the U.S. reported its first omicron case on Dec. 1. While some patients had recently traveled to southern Africa, others had no travel history. That suggests that community transmission is underway.