Course 10.2Lesson 3 of 3
The immune system recognises and kills microbes. A vaccine gives it practice with a harmless form of the microbe, so that it acts quickly later. Edward Jenner began vaccination with cowpox against smallpox. When many people are vaccinated, even the unprotected are safer. HIV is a case of a disease that attacks the immune system itself.
This lesson is free to read. Enroll free to keep your place and take the tests.
Try the code and the simulations beside the lesson.
Every day, microbes enter your body. You do not fall ill every day. The reason is your immune system.
The immune system is a set of cells and organs that find and kill microbes. Its main fighters are the white blood cells. When a microbe enters, white blood cells find it, kill it, and make special molecules called antibodies against it. Inflammation and fever are part of the same defence.
When a microbe is met for the first time, the body is slow. It takes several days to make enough defenders. In that time the microbe multiplies and the person may become ill. But the immune system remembers. If the same microbe comes again, the defenders are made much faster, and the microbe is killed before it can make us ill.
This is why most of us fall ill with measles only once. After the first time, the body is ready.
Immunisation uses this memory. A vaccine is a harmless form of a microbe: a dead or weakened germ, or a part of it. It cannot make us seriously ill. But the white blood cells meet it, learn it, and remember it.
When the real microbe comes later, the body is ready. The defenders act at once, and the microbe is killed before it spreads. The person does not fall ill, or falls only mildly ill.
One vaccine protects against one disease. A vaccine for measles will not protect against tetanus, because the memory is of one particular microbe.
Smallpox was a deadly disease caused by a virus. Many people died of it, and those who survived were often scarred for life.
In the 1790s, an English doctor named Edward Jenner noticed that milkmaids who had caught the mild disease cowpox from cows did not catch smallpox. In 1796 he took material from a cowpox sore and scratched it into the skin of a boy. The boy had a mild illness. Later he was exposed to smallpox, and he did not fall ill.
Jenner had discovered the first vaccine. The word comes from vacca, the Latin word for cow. By a worldwide effort of vaccination, smallpox was wiped out of the world. In 1980 the World Health Organization declared it eradicated. No person has caught it naturally since.
Today, vaccines protect against many diseases, and children in India are given them in a schedule from birth. These include:
Vaccines are only for diseases where a vaccine has been made. There is a vaccine for polio. There is none in general use against AIDS or malaria, so prevention has to depend on other ways.
An ill person is a problem for the family. Many ill people are a problem for the whole town. Public health means protecting the health of whole communities.
A community needs:
A vaccinated person is protected, and also helps others. When a microbe finds few people it can infect, it spreads slowly or not at all. So each vaccinated person makes the unprotected people around them safer: babies who are too young for a vaccine, and people who are too ill to have one. This protection of a whole community is called herd protection.
Look at it in the model. One pupil comes to school ill, and some of the class are vaccinated.
Start with % vaccinated, and many pupils fall ill. Raise the share and the number of ill pupils falls. A vaccinated pupil cannot be infected, so the infection has fewer places to go. With most of the class vaccinated, the infection stops almost at once.
AIDS stands for Acquired Immuno-Deficiency Syndrome. It is caused by the human immunodeficiency virus, or HIV.
HIV is different from most infections. It attacks the white blood cells, which are the defenders themselves. As more of them are destroyed, the immune system weakens. Such a person may die not from HIV itself, but from a common cold or a stomach upset that the body can no longer fight, such as pneumonia or tuberculosis.
How HIV spreads.
How HIV does not spread. It does not spread by touching, hugging, shaking hands, sharing food or cups, mosquito bites, or sitting beside an infected person. People with HIV need kindness and support, not fear.
How to prevent it. Use blood from tested donors, and a new, sterile needle for every injection. Mothers who are infected should be treated during pregnancy, so that their babies stay safe. Medicines can keep the virus under control for many years, but they cannot yet remove it from the body.
The program makes a class of 12 pupils again. It runs trials for each case, and says how many pupils fall ill on average. Each ill pupil infects each healthy and unvaccinated pupil with a chance of % each day.
You should see the average number of ill pupils fall as more are vaccinated. Each protected pupil is one less person the illness can reach.
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
Every lesson is open to read. Enrolling also lets you:
Log in to join the discussion.
Loading…