Dr. Brian Monahan, the attending physician of the U.S. Congress, told Senate chiefs of staff, staff directors, administrative managers and chief clerks from both parties on Tuesday that they should prepare for the worst, and offered advice on how to remain healthy.

Between the lines: Forecasting the spread of a virus is difficult, and the range of realistic possibilities is wide.

But other estimates, including statistical modeling from Harvard epidemiologist Marc Lipsitch, have said that somewhere between 20% and 60% of adults worldwide might catch the virus.

Yes, but: These estimates include people who will get sick and make a full recovery, and many people will catch the virus without ever feeling seriously ill.