Delta variant accounts for 93% of US COVID-19 cases, CDC estimates

What to know about the delta variant

The delta variant became the dominant strain of COVID-19 in the U.S. in the summer of 2021, driving up cases and hospitalizations.

The delta variant of COVID-19 accounts for 93% of cases in the United States, according to an estimate by the U.S. Centers for Disease Control and Prevention.

CDC data shows the primary delta variant, known as the lineage B1.617.2, makes up 83.4% of COVID-19 cases. But when combined with its sublineages, that number grows to 93.4%.

The AY.3 sublineage equals 9.1% of cases, the AY.2 makes up 0.8% and the AY.1 accounts for the remaining 0.1%.

57e4ab6d-COVID-19 Testing Site Run By State In Reading Pennsylvania

A sign that reads "Free COVID-19 Testing" at the state-run free COVID-19 testing site set up on Front Street in Reading, PA outside FirstEnergy Stadium Tuesday morning Oct. 13, 2020. (Photo by Ben Hasty/MediaNews Group/Reading Eagle via Getty Images)

The CDC calculated the numbers through its national genomic surveillance program, which is tasked with identifying new and emerging COVID-19 variants. Using data from genomic sequencing, the CDC groups sequences with similar genetic changes associated with important epidemiological and biological events into lineages.

Earlier this year, experts began labeling linages with the Greek alphabet. Before that, they were identified by the country in which they first appeared.

The delta variant was originally documented in India, the alpha variant in the United Kingdom, the beta variant in South Africa, and the gamma variant in Brazil.

More recently, the World Health Organization has labeled the lambda variant as a "variant of interest." It was first identified in Peru last year.

The CDC continues to stress the importance of being vaccinated against COVID-19. All three of the FDA-authorized vaccines continue to offer protection against all known variants of the virus.

The more infectious delta variant began driving COVID-19 cases higher earlier this summer and even caused a rise in breakthrough cases — which is when a fully vaccinated person becomes infected.]

Even so, fully vaccinated people have been far less likely to require hospitalization or die due to the virus. The CDC said less than 1% of breakthrough cases in the U.S. have resulted in hospitalizations or deaths.

More to the point, the CDC has stressed unvaccinated people account for more than 99% of recent hospitalizations and deaths in data collected between January and June.

Dr. Rochelle Walensky, the director of the CDC, said officials are working to collect more recent data since the delta variant began driving the surge. But she stressed unvaccinated people still make up the overwhelming majority of hospitalizations and deaths.

The White House has characterized this summer’s surge as preventable and a "pandemic of the unvaccinated."

In light of the summer surge, many businesses and schools have begun requiring proof of vaccination from employees and students.

This story was reported from Atlanta.