As a medical oncologist, Dr. Michael Grant’s patients fall into this group. He spoke with us about how he protects his patients from pneumonia and what he suggests when they have unexplained symptoms.

Your body might be sending you hints about your health.

How does the same infection, say the flu or a cold, give some people mild symptoms and leave others suffering? Why do people develop autoimmune diseases? And will we ever be able to predict when—and ...