(CNN) -- The Delta variant of Covid-19 is expected to become the dominant strain in the United States, and it's further reason why people need to ramp up the vaccination pace, said the director of the US Centers for Disease Control and Prevention.
In an interview with CNN on Friday, Dr. Rochelle Walensky said that the Delta variant's increased transmissibility could allow it overtake the Alpha variant, first identified in the United Kingdom, in the US in the coming months.
"The UK variant was more transmissible. That is now nearly 70% of the virus here," she said. "We know that the Delta variant is even more transmissible than the UK variant, and I anticipate that will be the predominant variant in the months ahead."
Walensky reiterated that the Pfizer/BioNTech and Moderna vaccines offer good protection against the variant — after the second dose.
"After two doses — reminding you, get your second dose — after two doses, you are protected from that Delta variant," she said. "And studies are underway now to examine the Johnson & Johnson. We just don't have as much data with that vaccine."
Another vaccine expert says that time is running out to get ahead of the potential strain of variants — as odds stack against the US reaching President Joe Biden's goal of 70% of adults at least partially vaccinated by July 4, especially as demand drops off.
"Vaccines are our only way out of this," Dr. Paul Offit told CNN's Wolf Blitzer. "Unless we vaccinate a significant percentage of the population before winter hits, you're going to see more spread and the creation of more variants, which will only make this task more difficult."
Cases and infections have decreased, Offit said. But with hundreds of people dying and at least 10,000 people infected most days, the rates are still too high to prevent the summer lull from turning into a winter surge, he said.
13 states have fully vaccinated more than half of residents
More than 44% of the US population is fully vaccinated, or 148.5 million people, according to the latest data from the CDC.
At least 13 states have fully vaccinated more than half of their residents. Those states are Connecticut, Hawaii, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New Mexico, New York, Oregon, Rhode Island, Vermont and Washington.
While the pace of vaccinations across the country has slowed, more than 900,000 new people on average become fully vaccinated daily, according to the CDC data.
In California, health officials announced the launch of a new website where residents can access a digital version of their Covid-19 vaccination card and use as proof of immunization -- but they said the electronic record will not be mandated.
"While (the California Department of Public Health) recommends that vaccinated Californians keep their paper CDC card in a safe and secure place, we recognize that some people might prefer an electronic version," California state epidemiologist Dr. Erica Pan said in a statement. "And if one of the state's nearly 20 million vaccinated Californians misplaces their paper card, the Digital COVID-19 Vaccine Record provides a convenient backup."
Variants should encourage people to get vaccinated, experts say
Experts have cautioned that the continued spread of the virus could lead to more numerous — and potentially more transmissible and dangerous — variants.
The US has already seen surges of the highly transmissible Alpha and Delta variants, while the spread of the Gamma variant is growing in several states.
To attain herd immunity, or the point at which the virus cannot easily spread within the community, experts have offered estimates of it requiring the inoculation through infection or vaccination of between 70 to 85% of the population. According to the CDC, only 53% of the population has received at least one dose of the vaccine.
And only 65% of adults have received at least one dose.
"You would have thought at the beginning of this, knowing that vaccines are our only way out of the pandemic, the hardest part would have been figuring out how to construct these vaccines," said Offit, a key member of the Food and Drug Administration's Vaccines Advisory Committee. "The hardest part is convincing people to get it, which is remarkable."
Spreading variants shouldn't be a concern to those who are vaccinated, Dr. Anthony Fauci told NPR, but it should be an incentive to get vaccinated.
The CDC elevated the Delta variant to a variant of concern this week. Fauci said that "the combination of more transmissibility and greater severity of disease, appropriately, prompted the CDC to elevate it to a variant of concern."
When asked how concerned he was about the variant, Fauci said: "I'm not concerned about the people who are vaccinated. Because the good news about all this, among the seriousness of the situation with regards to the variant, is that the vaccines work really quite well."
People who are vaccinated are protected, "which is another very good reason to encourage people strongly to get vaccinated because if you are not vaccinated, you are at risk of getting infected with a virus that now spreads more rapidly and gives more serious disease," said the director of the National Institute of Allergy and Infectious Diseases.
Vaccine protection could last a year or much longer
Experts and officials are pressing for people who are still hesitant to get the vaccines and help slow the spread.
"What do we do if a critical percentage of this population chooses not to get vaccinated and chooses to allow this virus to continue to spread, continue to hurt themselves and others and continue to create variants which become all the more contagious and all the more difficult to contain," Offit said.
Protection offered by vaccines appears to be very strong, Offit said.
"Although immunity might fade for protection against mild disease or asymptomatic infection or low moderate disease, I think protection against critical disease will probably be relatively long-lasting, meaning for a few years," he said. "The so-called cellular immune response induced by these vaccines appears to be excellent."
But experts can only rely on six months of data, since the vaccines are so new. And scientists still can't say for sure how long the protection will last.
Their durability will determine whether the population will need boosters, Fauci said.
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