After years of good health, Jacob finally visited the doctor for the first time in a decade. Immediately after his doctor' s appointment, Jacob fell ill with the flu. Each of the following, if true, explains the apparent paradox, EXCEPT: ["It was below freezing during the week before his doctor's appointment, and Jacob did not wear his winter coat.", "Jacob's flu was dormant and didn't show symptoms until after the doctor's visit.", "Jacob's immune system did not worsen after the doctor's visit.", "Jacob's doctor administered him several vaccines that temporarily weakened his immune system."]