baltimore health commissioner, dr. leana wen. author of "lifelines: a doctor's fight for public health." can you explain what general powell's pre-existing conditions may have done to his immune system? >> of course, anderson, we have to keep in mind that risk is additive. and general powell had at least two major risk factors for severe outcomes to covid-19. the first is age. an analysis of cdc data from august found that even if you are fully vaccinated, people in their 8 0z have a 15-times higher risk of dying of covid than a 50-year-old. and then, you have multiple myeloma which is a blood cancer that, by itself, substantially increases the risk of infection. and treatments to multiple myeloma, too, include chemotherapy, steroids, things that further suppress the immune system. and so, this is an -- an individual who unfortunately was at very high risk for contracting covid-19 by virtue of having a suppressed immune system that may not respond as well to vaccines.