As high as the coronavirus numbers seem, the CDC said Thursday, they're probably an underestimate. Only 10% of the nation's coronavirus cases have been diagnosed, the agency's director told reporters. With 2.3 million confirmed cases so far, that would mean more than 20 million Americans have been infected, NBC News reports. A review of coronavirus antibodies in blood samples led the CDC to the revision. "Our best estimate right now is that for every case that's reported, there actually are 10 other infections," said agency chief Dr. Robert Redfield. It's another example of the baffling nature of the disease. "This virus causes so much asymptomatic infection," Redfield said. "The traditional approach of looking for symptomatic illness and diagnosing it obviously underestimates the total amount of infections."
The CDC also changed its guidance on who's most vulnerable to serious illness from the virus on Thursday. There's no particular threshold at age 65 anymore; risk progressively increases with age, the agency said. Citing new evidence, the CDC added to the list of chronic conditions (such as obesity and kidney disease) that put people in greater danger if they contract the virus. About 60% of adults have one such condition. "While we are all at risk for COVID-19, we need to be aware of who is susceptible to severe complications so that we take appropriate measures to protect their health and well-being," Redfield said in a statement. As much as 95% of the US population is still susceptible to the coronavirus, he told reporters, per the Washington Post. The current rise in cases is attributable mostly to young people in the South and West, Redfield said. (Read more coronavirus stories.)