As of July 3, the latest date for which data was available, the delta variant accounted for 51.7% of new COVID-19 cases that had been genetically sequenced in the country. Two weeks earlier, on June 19, the variant accounted for just over 30% of new cases.
During a news briefing Tuesday, President Joe Biden cited the delta variant's rapid spread to urge people to get vaccinated, "especially young people who may have thought that they didn't have to be vaccinated, didn't have to worry about it, didn't have to do anything about it."
"This should cause everybody to think twice," Biden said.
Studies have shown that the COVID-19 vaccines are effective against multiple variants, including the delta variant. A recent report from Public Health England, where delta accounts for more than 90% of new cases, found two doses of the Pfizer vaccine to be 96% effective against hospitalization.
In addition to the U.S., the delta variant has been detected in 103 countries and is predicted to become the dominant variant globally.
"Based on the estimated transmission advantage of the delta variant, it is expected that delta will rapidly outcompete other variants and become the dominant circulating lineage over the coming months," the World Health Organization said Tuesday.
Worldwide, the number of new COVID-19 cases has increased slightly over the past two weeks, after a seven-week decline, according to the WHO. COVID-19-related deaths, however, continued to decline, reaching the lowest point since October 2020.
This story was originally published on NBC News.