The delta variant of the coronavirus that once crippled India now accounts for 20 percent of infections in the United States, Anthony Fauci, M.D., director of the U.S. National Institute of Allergy and Infectious Diseases, said Tuesday.

The percentage of the highly transmissible and potentially more dangerous variant doubled in recent weeks, Fauci said Tuesday at a White House briefing on the virus, CNN reported. "As was the case with [the alpha variant first seen in Britain], we seem to be following the pattern with the delta variant, with a doubling time of about two weeks," he noted.

Luckily, the Pfizer and Moderna vaccines appear effective against the delta variant, Fauci said, but the challenge is to get more people to take the vaccines, CNN reported. The Pfizer vaccine was 88 percent effective in preventing COVID-19 symptoms from the delta variant two weeks after the second dose of the vaccine.

"When you look at hospitalizations, again, both the Pfizer-BioNTech and the Oxford AstraZeneca are between 92 and 96 percent effective against hospitalizations," Fauci said.