A coronavirus variant first identified in India is "like Covid on steroids," Andy Slavitt, former White House senior adviser for Covid-19 response, said Wednesday.
"(The Delta variant) is a more virulent strain," Slavitt told CNN. "This is like Covid on steroids. You can be around people for less time and still get exposed."
The Centers for Disease Control and Prevention has labeled the Delta variant a "variant of concern," a designation given to strains of a virus that scientists believe are more transmissible or can cause more severe disease.
The CDC says the variant accounts for about 10% of coronavirus cases in the United States.
Slavitt said the variant provides people with one more reason to get vaccinated.
"If you have been vaccinated, you have very little to worry about," he said.
Surgeon General Vivek Murthy told CNN on Tuesday the Delta variant "is rapidly increasing here in the United States."
He said there is data that indicates it might cause more severe illness.
"That still needs to be understood more clearly, but these are two important concerns and they explain in part ... why this has become the dominant variant in the UK, where over 90% of cases are the Delta variant," Murthy said.
The good news is that vaccines appear to be effective against the variant.
A new study by Public Health England found that two doses of a coronavirus vaccine are "highly effective against hospitalization" caused by the variant. The study found the Pfizer/BioNTech vaccine is 96% effective against hospitalization after two doses.
Pfizer CEO Albert Bourla said during CNBC's Evolve Global Summit that he feels "very good" about the vaccine when it comes to variants of concern, but the company has a system in place in case a variant emerges that requires a more tailored vaccine.
Murthy said there isn't enough data to indicate the effectiveness of Johnson & Johnson's one-dose vaccine in regard to the Delta variant, but the vaccine has shown it can help prevent hospitalizations and deaths when people are infected with other strains.
"The key is get vaccinated, get both doses," Murthy said.
As of Wednesday, 44.1% of the total US population was fully vaccinated while 52.7% has received at least one dose of a vaccine, according to the CDC.
Thirteen states -- with the addition of Hawaii on Wednesday -- have fully vaccinated more than half of their residents, the CDC says.
This comes on the heels of the US surpassing 600,000 deaths since the coronavirus pandemic began, according to data compiled by Johns Hopkins University. That means about one in every 550 people in the US has died from the virus.