How Safe Are Vaccines?

Parents are opting out of shots for their kids. What the science says about the risks—and what you should do

Dan Habib / Concord Monitor / Corbis

Six-week-old Gavin Hubbard of New Hampshire bravely faces his series of five immunizations in the comforting grasp of Mom.

Correction Appended: May 29, 2008

Life, if you're a bacterium or virus, boils down to this: finding a pristine human home to provide for your every need, from food and nutrients to shelter against biological storms. As a microbial drifter, you can literally travel the world, hopping from host to host when the opportunity presents itself or when conditions at your temporary residence start heading south. There's no worry about taking along life's necessities either—viruses in particular are adept at traveling light; incapable of reproducing on their own, they think nothing of co-opting the reproductive machinery of their...