In addition to smallpox, the characters discuss diseases such as typhoid, tetanus, and polio, as well as anthrax. Although the symptoms vary from disease to disease, the diseases are similar in their ability to attack and terrify a vulnerable population. As Mitty studies his disease, he can’t help but feel some of the symptoms he is reading about, even when it would be too soon after exposure to feel any symptoms if he had smallpox. As he walks around New York, he imagines people around him swelling with pustules, the telltale marks of smallpox. Later, when he pretends to have smallpox to fool the terrorists, he fakes the appearance of certain symptoms by forcing himself to believe he really has the disease. His psychosomatic symptoms trick the terrorists into believing he is sick.

Rather than giving in to imaginary symptoms and hallucinations, scientists face the disease rationally and with purpose. The book discusses how scientists work to protect the population from these diseases by coming up with treatments and vaccines. Like those on the front lines in war, they are on the front lines of disease, heroically fighting these viruses, doing all they can to capture the disease.