Diphtheria is a bacterial infection that causes a thick gray coating at the back of the throat (the name comes from the Greek word for "leather hide") that makes it hard to breathe and swallow, and can result in suffocation, paralysis, and heart disease. One in 20 people who get the disease dies from it. Before the vaccine was developed in the 1920s, as many as 200,000 cases of diphtheria and 15,000 deaths were reported each year in the United States; these days there are about two cases per year, and only four children are known to have died from the disease since 1980. But each year sees outbreaks of diphtheria in Eastern Europe, Russia, Brazil, Nigeria, Indonesia, and the Philippines. While the risk of getting diphtheria in the United States is low, the disease is only a plane ride away.

Your child can get tetanus from stepping on a rusty nail or from any kind of puncture wound with a dirty object. It's a bacterial infection that causes severe and painful muscle spasms, seizures, and paralysis. Tetanus used to be called "lockjaw" because it can lead to locking of the jaw, making it impossible to open your mouth or swallow and causing death by suffocation in about 30 percent of the people who get it. Before the Second World War, when the vaccine came into widespread use, about 600 cases of tetanus and 180 deaths were reported each year in the United States. Now there are about 70 cases per year and 15 deaths, most of them in elderly adults. The disease isn't contagious, but because the tetanus bacterium lives in the soil, it will always be with us.

Pertussis, better known as whooping cough, is one of the most contagious diseases known to humans. It's a bacterial infection that causes coughing spells so bad it's hard for children to eat, drink, or breathe for weeks at a time. It can lead to pneumonia, seizures, brain damage, and death. Before the vaccine was introduced in the 1940s, about 200,000 children came down with the disease each year and about 8,000 died. About 7,000 cases of pertussis, including 10 deaths, are still reported in the United States every year, and the disease remains a serious health problem among children in other parts of the world.