When a human body is infected by a disease, the immune system of the body will be stimulated. The immune system will recognize the disease-causing germs as foreign invaders and will start to produce protein called antibodies. The role of the antibodies is to kill the disease-causing germs in our body,preventing us from becoming sick. The antibodies produced by the immune system will remain in our bloodstreams. When we are attacked by the same disease germs, the antibodies in the bloodstream can recognize them and destroy the germs before they have a chance to make us fall sick again.This is what we called immunity. There are many infectious disease that can be prevented by a vaccine. This is because a vaccine helps to develop the immunity in our body before we get sick.
Vaccine is an antigenic substance prepared from the causative agent of a disease. However, the disease causative agent in the vaccine are weakened so that they do not cause disease in our body. Furthermore, only a small amount of vaccine is required to activate and boost our body’s immune system. The immune system reacts to the vaccine by producing antibodies.The antibodies produced will destroy the germs present in the vaccine. Eventually,the antibodies produced will remain in our body,giving us immunity. If we are exposed to the real disease, these antibodies are ready to protect us from the disease by killing all the disease germs.
The yellow fever vaccine was discovered by Max Theiler. Max Theiler was a South African-American virologist and physician. In 1951, he was awarded the Nobel Prize in Physiology or Medicine for developing a vaccine against yellow fever.
Max Theiler started to develop a vaccine against yellow fever after he found that the yellow fever virus can be weakened by passing it from mouse to mouse. This finding formed the basis of two separate vaccines. The first vaccine was a weakened strain that used by the French government to protect their residents in Western Africa in 1930s and 1940s. The second vaccine was an improved version of the first vaccine which is known as 17D. This vaccine was grown in chicken embryos and was more effective since it was easier to produce. This vaccine was easily adapted for mass production and became the universal standard.
He also found that the weakened yellow fever virus that was passed into laboratory mice conferred the immunity on Rhesus macaques, which is a species of small monkey. In fact, monkeys served as the primary experimental animals before mice are used. The availability of mice help to reduce costs, improve efficiency and produce a vaccine. After the discovery of susceptibility of mice to the yellow fever virus, Theiler devised a test to detect the yellow fever antibodies in the sera of the mice. This test enable the development of human yellow fever vaccine. In the test, Theiler mixed 13 yellow fever immune sera of mice with equal quantities of centrifuged suspension of infective mouse brain.The mixture is then injected intracerebrally into mice. This test showed the presence of protective action in all 13 sera. This also indicates the presence of protective antibodies in the mice. As a result, most of the mice are able to survive because of the protective antibodies present in their body.