The US is “at another pivotal moment in this pandemic” as rising Covid-19 cases show no signs of abating, driven by the Delta variant, and some hospitals are filling up, especially in areas with low vaccination rates, government officials warned on Thursday. The US government did not change its guidance on mask wearing, despite debates going on in the White House and the Centers for Disease Control and Prevention (CDC) about whether those who have been vaccinated should once again be officially advised to wear masks indoors to prevent the spread. Rochelle Walensky, director of the CDC, said that the Delta variant of coronavirus “is now spreading with incredible efficiency” in the US and that, compared with the original coronavirus strain that broke out in the US in early 2020, this variant is “more aggressive”. “It is one of the most infectious respiratory viruses we know of and that I have seen in my 20-year career,” she said at a White House briefing on Thursday, noting that the US is “not out of the woods”. Walensky warned: “We are at another pivotal moment in this pandemic, with cases rising again and some hospitals reaching their capacity in some areas.” The US is far from the dire situation before the vaccines were widely available, when repeated surges of infections in 2020 drove the US death toll in the pandemic above 600,000, the highest in the world. But officials are becoming concerned as new cases have continued to rise fast in the last two weeks and vaccination rates are stuck stubbornly just below Joe Biden’s 4 July goal of 70% of American adults having had at least one shot. The Delta variant now accounts for more than 83% of new coronavirus cases in the US. And Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and the chief medical adviser to the president, said there are some areas of the country where Delta accounts for more than 90% of new infections. “And if you look at the recent seven-day or 14-day averages of cases, for example, the cases are up by, like, 195%. The hospitalizations are up 46%. And the 14-day average for deaths are up 42% … it’s not the direction we want it to be,” Fauci told NPR News, adding: “We’ve got to do much better.” A smiling and unmasked Biden in May hailed a “great day” and said that “if you are fully vaccinated, you no longer need to wear a mask” or practice social distancing. But the US president is now almost daily urging eligible Americans who have not been vaccinated to get the shot, saying on Wednesday night that it was “gigantically important”. On Thursday, when Walensky was asked if official mask guidance had changed she said it had not. “Fully vaccinated people are protected from severe illness,” she said but added that in areas with high numbers of cases, low vaccination rates and where the Delta variant is rising “you should be wearing a mask if you are unvaccinated. If you are vaccinated you get exceptional protection from the vaccine but you have the opportunity to make the personal choice to add extra layers of protection if you so choose.”