Evan Brown, age 9, of Erie, Pa., for his question:

WHO GAVE THE FIRST VACCINATION?

A vaccination is the introduction of weakened or dead viruses or bacteria or their poisons into the body to develop resistance to  disease. Edward Jenner introduced the vaccination as a preventative measure against smallpox in 1796. Jenner was an English doctor.

Material introduced into the body with a vaccination is called a vaccine. Vaccines must be strong enough to cause the body to develop resistance but weak enough so they will not infect the body or cause serious illness.

Effective vaccines have been developed against cholera, diphtheria, German measles, influenza, measles, rabies, Rocky Mountain spotted fever, smallpox, lockjaw, typhoid and paratyphoid, typhus and yellow fever.

Most vaccines are injected into the body, although the Sabin polio vaccine is taken by mouth. Vaccination comes from the Latin word "vacca," meaning "cow." The term originally referred to the injection of cowpox virus to prevent smallpox.