EXCLUSIVE: The Centers for Disease Control and Prevention on Tuesday will announce that the delta variant of COVID-19 is a “variant of concern” in the U.S., but that two doses of the Pfizer and Moderna vaccines are effective against it, Fox News has learned.Labeling delta a “variant of concern” is a change officials say is based on “mounting evidence” that the variant spreads more easily and causes more severe cases when compared to other variants.Biden administration officials said that they are studying the effectiveness of Johnson & Johnson’s one-dose vaccine and “remain optimistic,” as overseas, the AstraZeneca vaccine has demonstrated effectiveness against delta. An official told Fox News the AstraZeneca vaccine is “built on a similar platform as Johnson & Johnson.” A CDC web page last updated Monday now shows delta among “variants of concern,” though officials are alerting to the public to the change Tuesday.The official told Fox News that vaccinated people have a “high degree of protection,” but warned that those who are not vaccinated “are at risk.”The CDC’s classifications define three classes of variants of COVID-19 – variants of interest, variants of concern, and variants of high consequence. According to the CDC, a variant’s classification status can change as officials learn more about them. “CDC and SARS-CoV-2 Interagency Group continually review the available scientific evidence and the genomic surveillance data to assess the classification of variants,” the CDC said. According to the CDC, “variants of concern” may require several public health actions, like notifying the World Health Organization under International Health Regulations, reporting to CDC, local or regional efforts to control the spread, increased testing, or research to determine the effectiveness of vaccines and treatments against the variant. “Based on the characteristics of the variant, additional considerations may include the development of new diagnostics or the modification of vaccines or treatments,” the CDC said, adding that “investigations are underway to further characterize this variant of concern and its potential effect on current vaccines and treatments (therapeutics.)CLICK HERE TO GET THE FOX NEWS APPIn light of the CDC’s upcoming announcement, a Biden administration official highlighted the importance of getting vaccinated, saying it is the “best way to fully protect against variants.” “It is easier than ever to get vaccinated,” the official told Fox News. According to officials, 64.5% of adults in the United States have received at least one dose of a COVID-19 vaccine.