About a third of people infected with coronavirus in the US are asymptomatic, according to newly released guidance from the Centres for Disease Control and Prevention. The CDC and the Office of the Assistant Secretary for Preparedness and Response have developed five different planning scenarios to help public health officials making coronavirus decisions based on mathematical modelling. To determine each scenario, the CDC looks at “measures of viral transmissibility, disease severity and pre-symptomatic and asymptomatic disease transmission.” An “asymptomatic case” means that an individual infected with the virus “does not exhibit symptoms during the course of infection.” According to the most updated information, and under CDC’s “best estimate about viral transmission and disease severity in the United States,” the agency believes that 35 per cent of people infected by the coronavirus show no symptoms – but are nonetheless capable of spreading the virus. The agency also estimates that – under that same scenario – about 0.4 per cent of people who contract the virus will die from it. According to the CDC’s worst-case scenario, the case fatality rate jumps to 1 per cent. US CDC had ‘very good interaction with China’ after coronavirus outbreak Carl T Bergstrom, a biologist with the University of Washington, says the numbers are too optimistic. “With guidance from this newly released CDC document, federal agencies are modelling the Covid pandemic using implausibly low fatality rate,” he tweeted. With guidance from this newly released CDC document, federal agencies are modeling the COVID pandemic using implausibly low fatality rate. Their "best estimate" has a symptomatic CFR of 0.4% Their worst case scenario has CFR — not IFR — of 1% https://t.co/E34k5kzZSG pic.twitter.com/C4tGpsykHj — Carl T. Bergstrom (@CT_Bergstrom) May 21, 2020 “As I see it, the ‘best estimate’ is extremely optimistic, and the ‘worst case’ scenario is fairly optimistic even as a best estimate. One certainly wants to consider worse scenarios,” Bergstrom, an expert in modelling and computer simulations, told CNN. Under CDC’s best scenario, 3.4 per cent of infected people will require hospitalisation, a figure that substantially rises for the elderly population: 7.4 per cent of individuals 65 and older will need to be treated at a hospital. The agency also noted that 40 per cent of coronavirus transmissions occur before people get sick.