Lifestyle Health Delta Variant Is Now the Most Common COVID Strain in the U.S., CDC Says The CDC reports that the highly contagious Delta variant makes up for 51.7% of COVID cases in the U.S. as of Saturday, up from 30.4% two weeks prior By Jen Juneau Jen Juneau Twitter Jen Juneau is a digital news writer for PEOPLE. A '90s teen and horror film connoisseur, she started at the brand in 2016, after a decade of working as a technical writer and then moonlighting as a journalist beginning in 2013. Originally from New Orleans, Jen grew up both in NOLA and Florida and eventually attended the University of Central Florida in Orlando (still her home base!), where she earned a bachelor's in English/technical communication, with a minor in magazine journalism. People Editorial Guidelines Published on July 7, 2021 10:03 AM Share Tweet Pin Email Travelers head to the airport wearing masks. Photo: Paul Hennessy/SOPA Images/LightRocket via Getty The Delta variant is now the most common form of the COVID-19 virus circulating in the United States, according to new data from the Centers for Disease Control and Prevention. The CDC reports that the highly contagious strain, also known as B.1.617.2, makes up for 51.7% of COVID cases in the U.S. as of Saturday, up from 30.4% two weeks prior. Previously, the Alpha variant made up the majority of U.S. COVID-19 cases, but it now sits at just 28.7% as opposed to the Delta strain's 51.7%. According to the CDC, the area with the highest rate of the Delta variant (80.7%) in circulation is the HHS Region 7, comprising Iowa, Kansas, Missouri and Nebraska. Republican Governor Says Partisan Divide to Blame For Low Vaccination Rates: "Politics is Becoming Religion" Dr. Anthony Fauci, the nation's top infectious diseases expert, said last week that he's "very concerned" about the Delta variant spreading in under-vaccinated, high-risk areas, and added that it could split the country into "two Americas": one in which the virus is circulating widely and the other with low rates because most residents are vaccinated. "When you have such a low level of vaccination superimposed upon a variant that has a high degree of efficiency of spread, what you are going to see among under-vaccinated regions — be that states, cities or counties — you're going to see these individual types of blips," he said, CNN reported. "It's almost like it's going to be two Americas." News of the Delta variant's dominance comes days after news that the Johnson & Johnson single-dose vaccine can now provide immunity against COVID-19 for at least eight months, as well as protection against "other highly prevalent SARS-CoV-2 viral variants" of the virus. The company announced on Thursday that during its trial, the vaccine generated a "strong neutralizing antibody response" to the widely spreading Delta variant, with 85% effectiveness. RELATED VIDEO: Nurse Whose Husband Died of COVID Is on a Door-to-Door Vaccine Crusade: "I Can Help Save Others" It is also expected to improve and continue immunity past the eight-month span of their study — reassuring the millions of Americans who have gotten the Johnson & Johnson dose. "Current data for the eight months studied so far show that the single-shot Johnson & Johnson COVID-19 vaccine generates a strong neutralizing antibody response that does not wane; rather, we observe an improvement over time," said Mathai Mammen, global head, Janssen research & development, Johnson & Johnson, in a statement. "In addition, we observe a persistent and particularly robust, durable cellular immune response." The Johnson & Johnson study follows the lead of Moderna and Pfizer after the biotech companies also announced that their vaccines are extremely effective against the Delta variant, preventing illness 90% of the time and hospitalization or severe illness 94% of the time. As of Wednesday morning, nearly 183 million Americans (55% of the total population) have received at least one COVID-19 vaccine dose and 157.6 million (47.5%) are fully vaccinated, according to the CDC. As information about the coronavirus pandemic rapidly changes, PEOPLE is committed to providing the most recent data in our coverage. Some of the information in this story may have changed after publication. For the latest on COVID-19, readers are encouraged to use online resources from the CDC, WHO and local public health departments. PEOPLE has partnered with GoFundMe to raise money for the COVID-19 Relief Fund, a GoFundMe.org fundraiser to support everything from frontline responders to families in need, as well as organizations helping communities. For more information or to donate, click here.