A vaccine is something that helps protect you against a disease. Usually it contains a very small amount of some substance which is similar to the disease. This teaches the body to fight it. If you get infected by the disease, the body recognises it and goes to war with it. Interestingly, the word 'vaccine' is related to the word 'cow'. The Latin word for cow is vacca. It was used to make the English word 'vaccine' because of how vaccines were discovered.
Back on the farm
In the 18th century a disease called smallpox was killing around 400,000 people every year. People who did not die of it often went blind. People who did not go blind were left with horrible scars from the pimples the disease caused all over their bodies.
In 1796, Edward Jenner, an English doctor, noticed that girls who milked cows never seemed to get smallpox. They did get another disease, though, from cows, called cowpox. Cowpox was much milder than smallpox. It didn't kill people and it did not leave scars. He realised that, if you gave people cowpox, they would not get smallpox.
And the chickens
The real breakthrough with vaccines was made by a Frenchman called Louis Pasteur. He is famous as the man who invented pasteurisation - what we do to milk to be sure there are no germs in it. In the late 19th century Pasteur was researching another deadly disease - cholera.
He was injecting it into chickens. But he accidentally injected the dead cholera virus into one group of chickens. They did not get sick. Later when he injected them with the live virus, they still did not get sick. He realised that the dead virus had taught their bodies to recognise it.
Not for everything
What Pasteur discovered is still used in many vaccines today - using dead virus as a vaccine. But it does not always work. We still do not have a vaccine for malaria. We do not have a vaccine for Aids.
Today, scientists are racing to make a vaccine for swine flu. Not everybody is sure they can. If the swine flu mutates - or changes - into something worse, maybe the vaccine we make now will not work.
now do this
1 The word vaccine is related to ...
a. Latin for swine
b. Greek for chicken
c. Latin for cow
2 In the 18th century ... was killing 400,000 people every year.
3 There is still no vaccine for ...
Answers on page 11 next Friday
Page 5: 1. c, 2. a, 3. b