The “Delta” coronavirus variant first discovered in India is raising some concerns in the U.S. as the number of infections caused by it doubles every week, according to former U.S. Food and Drug Administration commissioner Dr. Scott Gottlieb.

Gottlieb told CBS News’ “Face the Nation” on Sunday that Delta is “probably” going to become the dominant coronavirus strain in the U.S., making up about 10% of current infections and posing greater risks to communities with low vaccination rates.

“That doesn’t mean that we’re going to see a sharp uptick in infections, but it does mean that this is going to take over. And I think the risk is that this could spike a new epidemic heading into the fall,” Gottlieb told the outlet. “I think in parts of the country where you have less vaccination, particularly in parts of the South, where you have some cities where vaccination rates are low, there’s a risk that you could see outbreaks with this new variant.”

Last week, White House medical adviser Dr. Anthony Fauci said the Delta variant made up more than 6% of the sequenced coronavirus cases in the nation.

Emerging evidence from other countries, particularly the U.K. where it has become the dominant variant, shows Delta is more contagious, increases disease severity such as risks of hospitalization and is associated with a “modest” decrease in antibody activity in previously infected and vaccinated people compared to the Alpha variant, which first emerged from the U.K.

The Delta variant has been reported in about 60 countries, according to Fauci, and is “peaking” in people between 12 and 20 years old in the U.K.. “We cannot let that happen in the United States,” he said during a White House COVID-19 briefing on Tuesday.

A new study on over 19,500 coronavirus infections and 377 hospital admissions in Scotland found that people infected with the Delta variant were twice as likely to be hospitalized with COVID-19 than those sick with the Alpha variant. Researchers also learned the variant was mostly infecting young people and causing severe illness in those with other medical conditions.

Story continues

Doctors across the globe are noticing similar trends among their COVID-19 patients.

Up to 12% of patients in China infected with the Delta variant develop severe or critical COVID-19 within about four days after their symptoms start, The New York Times reported, compared to about 3% sick with the original version of the coronavirus. In general, people are becoming sicker more quickly and the levels of virus in their bodies are higher than previously observed.

Still, the COVID-19 vaccines are effective against Delta, despite being about 60% more contagious than the Alpha variant.

A study from Public Health England found that three weeks after one dose, the AstraZeneca and Pfizer-BioNTech coronavirus vaccines were 33% effective against symptomatic COVID-19 caused by the Delta variant compared to about 50% against the Alpha variant.

Two weeks following the second dose, which is recommended for full protection, the Pfizer vaccine was 88% and 93% effective against Delta and Alpha, respectively; the AstraZeneca shot, which has not been authorized for emergency use in the U.S., was 60% and 66% effective against Delta and Alpha, respectively.

Experts say the data emphasizes the importance of receiving all doses of a COVID-19 vaccine. More than 143.9 million Americans are fully vaccinated in the U.S., about 43% of the total population as of June 14, according to a Centers for Disease Control and Prevention tracker.

“We have the tools to control this and defeat it,” Gottlieb told CBS News. “We just need to use those tools.”

There are no studies to date that have tested how effective the Moderna or Johnson & Johnson COVID-19 vaccines are against the variant.

Some experts say the U.S. needs more data to correctly interpret how infectious the Delta variant really is because much of the data is coming from India, where variant tracking efforts aren’t as focused as in the U.K., for example.

“Preliminary results say you do see this increased transmissibility, but we still need to collect more information,” Nevan Krogan, a molecular biologist at the University of California, San Francisco told ABC News. “We need more data, and not just tracking and epidemiology data, but we also need molecular data. The more we understand about this virus and how it mutates, the better off we’re going to be in the future.”

The World Health Organization has added the Delta variant to its list of “variants of concern,” but the CDC has not.