The nation’s top public health agency on Thursday revamped its list of which Americans are at higher risk for severe COVID-19 illness, adding pregnant women and removing age alone as a factor. The CDC also changed the list of underlying conditions that make someone more susceptible to suffering and death. Sickle cell disease joined the list, for example. And the threshold for risky levels of obesity was lowered. The changes didn’t include adding race as a risk factor for serious illness, despite accumulating evidence that Black people, Hispanics and Native Americans have higher rates of infection, hospitalization and death.