The potentially deadly Delta variant that was originally identified in India is rapidly becoming the dominant virus in the U.S. and could wreak havoc in areas with low vaccination rates, say experts. Dr. Scott Gottlieb, a former commissioner of the Food and Drug Administration, said that 10% of current COVID-19 cases could be attributed to the virus formerly known as the B.1.617.2 variant, but the percentages of cases are doubling every two weeks.

According to CNN, Gottlieb, who served as the FDA chief from 2017 to 2019, said that Delta could become the dominant strain in the U.S. and could affect vulnerable regions in the country by fall.

“I think in parts of the country where you have less vaccination ― particularly in parts of the South, where vaccination rates are low — there’s a risk that you could see outbreaks with this new variant,” said Gottlieb. He told CNBC that “people who are full vaccinated, I think, are pretty well protected against this new variant based on accruing evidence.”

Gottlieb said that the big question is “are their enough unvaccinated people that this could get into the population and start spreading more widely? I happen to think it’s unlikely that this is going to be a threat until the fall.”

Gottlieb stressed that both doses of the two-dose COVID-19 vaccines are needed to protect against the Delta variant. “It does seem to be a more dangerous variant,” he told CNBC.

So far, the U.S. has administered 309 million doses of the COVID-19 vaccine nationally, but certain areas are at risk, said Gottlieb. Across the country, 64.4% of adults have received at least one dose of the vaccine but there are several states with a much lower immunization rate, according to CNN. For example, less than half of adults in Alabama, Louisiana, Mississippi, and Wyoming have received one dose, according to data from the Centers for Disease Control and Prevention.

For these people, the Delta mutation could pose a serious threat, said Gottlieb, because it is more transmissible than the previous variants. But he added that vaccines could prevent an uptick in COVID-19 cases caused by Delta.

“We have the tools to control this and defeat it, we just need to use those tools,” Gottlieb said, according to CNN.