Vaccines and Public Health

Immunization means helping the body build immunity against a disease. In active immunization, a person is given a vaccine, which contains a harmless piece of a pathogen called an antigen. This causes the body to produce a primary immune response, just like it would during a real infection. Sometimes a second dose, called a booster, is given later. This causes a faster and stronger secondary immune response, giving better protection. Scientists use different technologies to safely change or copy parts of pathogens so vaccines can trigger immunity without causing the disease.

Discovery of Vaccines

The first vaccine was developed during deadly smallpox epidemics. Smallpox killed about one third of the people who caught it. Before the late 1800s, people did not know what caused infectious diseases, but they noticed that survivors of smallpox rarely got it again. To try to protect themselves, some people practiced variolation, which meant putting material from smallpox sores into their skin to cause a mild infection. This sometimes worked, but it was very dangerous and many people died.

By the 1700s, people noticed that milkmaids who had caught cowpox, a mild disease, usually did not get smallpox. 

In 1796, British doctor Edward Jenner tested this idea by giving a boy material from a cowpox sore. Six weeks later, Jenner exposed the boy to smallpox, and the boy did not get sick. Even though this evidence showed the method worked, many people at first resisted using cowpox sores for protection. They did not understand how immunity worked and were afraid that putting material from a cow into the body was unsafe. Some people even believed it could cause strange side effects, like turning into cows. However, as more people were vaccinated and protected during smallpox outbreaks, and as studies confirmed Jenner’s results, the evidence clearly showed that cowpox vaccination was effective.

Today we understand why this worked. Cowpox and smallpox are caused by closely related viruses that have similar antigens, which are the surface markers the immune system recognizes. Because the antigens are so similar, the antibodies made during a cowpox infection could also recognize and fight smallpox. Since Jenner’s discovery, vaccines have been developed for many other diseases. Vaccines greatly reduce infections, suffering, and death. In many countries, childhood vaccination programs have nearly eliminated serious diseases such as measles.