The first vaccine was developed in 1796, by a British doctor, Edward Jenner. The word vaccine comes from a Latin word relating to cows. That's because the first vaccine was based on cowpox, a mild disease of cattle and people, but it also protected against the much more deadly smallpox virus.

If 9 in 10 children are vaccinated, the disease cannot spread far even if someone not vaccinated gets it. This is sometimes called "community" or herd" immunity. This means unvaccinated people are protected by the great number of others immune to the illness.

Before vaccines, the only way to become immune to a disease was to actually get it and survive it. Vaccines provide an easier and less risky way to become immune. A vaccine trains the immune system by appearing like a natural infection. A vaccine is made from a weakened live germ, killed germ, or parts of the germ.

Vaccines that contain inactivated toxins include the shots for tetanus and diphtheria. Another type of vaccine uses substances called polysaccharides from the cell wall to cause immunity.

The CDC recommends an annual flu shot for everyone 6 months or older.

You may also need other vaccines, depending on your health and lifestyle. Check with your healthcare provider. Because of the increasing number of whooping cough (pertussis) cases in adults, 2 booster vaccines are now available for adults. These vaccines protect against pertussis, diphtheria, and tetanus. Pregnant people may get a booster shot for whooping cough shortly before childbirth to protect their newborn.

The CDC recommends that all children who are 11 or 12 years old get a 2-shot series of the HPV vaccine at least 6 months apart. The vaccine series can start at age 9. The HPV vaccine is recommended for all adults through age 26 if they did not get vaccinated when they were younger. Teens and young adults who start the vaccine series between ages 15 and 26 need 3 doses of the HPV vaccine. In some people, the HPV vaccine may be advised between the ages of 27 and 45. Talk with your healthcare provider to learn more.

Most people who get vaccinated have no side effects from a vaccine. But mild reactions such as fever or soreness at the injection site can occur, the CDC says.