Health officials are urging COVID-19 vaccinations as the Delta virus variant, first detected in India, has climbed to comprise 6% of infections in the U.S. and appears to be spreading rapidly among young people in the U.K.

The strain has taken a dominant foothold in the U.K., though it has also been reported in 60 countries. Dr. Anthony Fauci, President Biden’s chief medical adviser, said during a White House briefing Tuesday that the Delta variant appears to spread more readily and may pose a greater threat, such as hospitalization risk, than the original, wild-type variant.

"However, fortunately, two doses of the Pfizer vaccine and AstraZeneca appear to be effective against the Delta variant," Fauci said. "There’s reduced vaccine effectiveness after one dose, however."

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Preliminary findings from Public Health England indicated two weeks post-second dose of Pfizer’s vaccine, there was an 88% effectiveness against the Delta variant. Three weeks after a single dose, the vaccines were 33% effective against symptomatic disease stemming from the Delta variant, underscoring the importance of a second dose, Fauci said.

In England, the highly transmissible B.1.1.7 strain has given way to the variant first identified in India.

"We cannot let that happen in the United States," Fauci continued, stressing the need to complete vaccination series. "For those who have been not vaccinated yet, please get vaccinated."

He reiterated Biden’s goal to reach 70% of adults with at least one shot by July 4.

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Dr. Jonathan Javitt, CEO of NRx and adjunct professor at Johns Hopkins School of Medicine, told Fox News that the Delta variant is just one instance of viral mutants to come threatening to reduce vaccine-induced protection.

"I think the Delta variant from India is one example of many ways this virus is going to mutate and attempt to circumvent the vaccines because that’s what viruses do," Javitt said, later adding, "Getting everybody to a baseline level of vaccination, of course, is critical."

Javitt emphasized the need for continued development of COVID-19 therapeutics to offer further protection in the small fraction of breakthrough cases, or illness cropping up in vaccinated individuals.

Currently, the CDC categorizes the Delta variant as one of "interest" versus one of "concern."