Lifestyle Health Delta Variant Now in All 50 States as L.A. Tells Vaccinated People to Continue Wearing Masks CDC Director Dr. Rochelle Walensky said that while the CDC's guidance on masks will not change, areas with “low vaccination rates” should consider reinstating mask requirements By Julie Mazziotta Julie Mazziotta Twitter Associate Editor, PEOPLE Health People Editorial Guidelines Published on July 1, 2021 04:20 PM Share Tweet Pin Email Travelers head to the airport wearing masks. Photo: Paul Hennessy/SOPA Images/LightRocket via Getty The highly contagious Delta variant of COVID-19 is now spreading in all 50 states and Washington, D.C., according to the Centers for Disease Control. South Dakota was the last state in the nation to report a case with the variant, finding its first on Tuesday. Nationwide, around 26% of all COVID-19 cases are from the Delta variant. Dr. Anthony Fauci, the nation's top infectious diseases expert, said Tuesday that he's "very concerned" about the Delta variant spreading in undervaccinated areas where people are at high risk, and said 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 undervaccinated 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." Fauci Says the Delta Variant Is the 'Greatest Threat' to Ending the COVID Pandemic in the U.S. Currently, 54.6% of all Americans have at least one dose of a COVID-19 vaccine, and 47% are fully vaccinated, according to the CDC. However, many states are outliers in that total. Vermont, Massachusetts, Connecticut, Maine and Rhode Island all have over 70% residents now fully vaccinated against COVID-19, while Alabama, Arkansas, Wyoming, Louisiana and Tennessee are at 44% or less, and Mississippi is at the bottom, with 38% fully vaccinated. RELATED VIDEO: Nurse Whose Husband Died of COVID Is on a Door-to-Door Vaccine Crusade: 'I Can Help Save Others' Globally, with the Delta variant circulating and lower rates of vaccinations, the World Health Organization has recommended that everyone, even those who are vaccinated, continue wearing masks indoors. That contrasts with the CDC's current guidelines, which allow for fully vaccinated people to forgo masks in nearly all indoor places. In response to the rise in cases with the Delta variant, and with the percentage of residents that are fully vaccinated hovering around 50%, Los Angeles County has advised that "everyone, regardless of vaccination status, wear masks indoors in public places as a precautionary measure." U.S. Health Secretary Says Unvaccinated People Are 'Vulnerable' to Highly Contagious Delta Variant CDC Director Dr. Rochelle Walensky, however, has said that the federal health agency does not intend to change its mask recommendations at this time. "We know that the WHO has to make guidelines and provide information to the world," she said on Today on Wednesday. "Right now, we know as we look across the globe that less than 15% of people around the world have been vaccinated, and many of those people have only received one dose of a two-dose vaccine. There are places around the world that are surging, and so as the WHO makes those recommendations, they do so in that context." With more Americans fully vaccinated, Walensky said that they are "really quite protected from the variants that we have circulating here in the United States." She added, though, that undervaccinated localities should consider increasing their mask guidance. "We've always said that local policymakers need to make policies for their local environment," Walensky said. "There are areas of this country where ... they have low vaccination rates, and there are areas that have more disease. ... So in those areas, we have always said please look, make suggestions."