英语听力—环球英语 1291 How Vaccines Work

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　　Welcome to Spotlight 1. I’m Mike Procter.
 
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　　And I’m Liz Waid. Spotlight uses a special English method of broadcasting. It is easier for people to understand, no matter where in the world they live.
 
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　　Today’s Spotlight program is about vaccines 3. These medicines are changing lives all over the world. But how exactly do they work? What are they? We will explore vaccines today on Spotlight.
 
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　　You may have heard our program about the history of vaccines. That program told about Doctor Edward Jenner.  He wanted to stop a disease called smallpox 4.  Smallpox was an ancient and deadly disease. It caused the death of many people. Doctor Jenner experimented with smallpox and cowpox. Cowpox is a disease that is very similar to smallpox. It mostly infects cows. But it can infect humans too. It is much less severe than smallpox. Doctor Jenner proved that if people became infected with cowpox, they would be immune 5 to smallpox. That is, they would not become infected with smallpox.
 
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　　Doctor Jenner’s research helped him to develop the first vaccine 2. Vaccination 6 is the process of placing particular infected material inside a person to help protect the body against diseases.
 
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　　Vaccines led to the end of the horrible disease smallpox.  Vaccines have also reduced the number of deaths from other diseases. Today, many governments require their people to have vaccinations 7. And some vaccines are provided for free.  Vaccines protect many thousands of people every year in many different countries.
 
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　　To understand what a vaccine does, we need to know a little about the immune system. Everyone has an immune system. This system helps to protect people from diseases. It is a complex system of organs and fluids. They work together to find and destroy viruses and bacteria inside a person’s body.
 
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　　A virus is a very small organism. A person cannot see it.  But this small organism can cause a lot of trouble. A virus invades a cell inside a person’s body. Then it uses parts of that cell to make copies of itself. Soon, there are many copies of the virus. Viruses can copy themselves thousands of times. So, infections can spread very quickly through a person’s body.
 
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　　The immune system tries to stop viruses with antibodies.  Antibodies are very important. Under a powerful microscope, an antibody looks like the letter Y. Each end connects with a different substance or molecule 8. When an antibody attaches to a virus, the virus cannot harm the body. Antibodies stop the virus from spreading. A person’s body makes a special antibody for each particular virus. That special antibody will attack that particular virus.
 
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　　Every antibody that a person needs for every different virus is already stored inside a person’s immune system.  It is stored as a kind of design plan, or blueprint 9. There are millions of different antibodies! And each antibody blueprint is already in your body! Your immune system just needs to find and copy it. But it can take a long time for the immune system to find and copy the antibodies.
 
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　　Imagine that a virus attacks a person’s body. The immune system immediately tries to find the right antibody blueprint. At the same time, the immune system tries to stop the viral infection through fever, pain and sickness. A person feels sick. He may have a fever. His body tries to use the heat from the fever to kill the virus. The person may be unable to eat or drink.
 
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　　In these ways the immune system actually makes the person feel sick! But this sickness has a purpose. These reactions from the person’s body try to slow the spread of the virus. This gives the person more time to produce the correct antibodies. When a person’s body cannot find and produce enough antibodies to fight the virus, they die.
 
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　　A vaccine is a generally a very weak form of a virus.  This weakened form of virus is usually injected into a person’s body.  A vaccine encourages the immune system to create antibodies for that virus. It shows the immune system what the virus looks like. So, if the real virus threatens the immune system, the immune system already has the correct antibodies to fight it.
 
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　　There are a few different kinds of vaccines. Scientists use each different kind depending on the virus they are attacking. Here are a few of them. One kind of vaccine is a “killed vaccine”. Scientists use a chemical, heat, or another method to kill the virus. Then they inject the dead virus into a person’s body. The immune system can create antibodies for the killed virus. Some polio and influenza 10 vaccines are examples of killed vaccines.
 
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　　Another kind of vaccine is a “subunit vaccine”. This vaccine uses only part of a virus. These are the parts of the virus that help the body become more immune. The hepatitis B vaccine is an example of a subunit vaccine.
 
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　　Scientists and doctors consider these two kinds of vaccines the safest. These vaccines are also usually less painful than other vaccines. They cannot cause disease in people with weak immune systems. But some of these vaccines are not permanent. Sometimes a person must receive a vaccination every few years to protect against these viruses.
 
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　　Another kind of vaccine is an “attenuated 11 vaccine”. Doctors believe these vaccines are the most effective. This is because they are live organisms. Often people who receive attenuated vaccines never need more vaccinations for that particular virus.
 
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　　But attenuated vaccines can do things that doctors do not expect. In a few extremely rare cases these live vaccines can change into the original virus. The vaccine could infect the person instead of protecting him. This does not happen very often. And doctors make sure that the vaccines are as safe as possible. There are attenuated vaccines for mumps 12, measles 13, and rubella.
 
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　　Killed, subunit, and attenuated vaccines are only three kinds of vaccines. There are other kinds of vaccines too. And scientists continue to work on new and better vaccines. But all vaccines do the same basic thing. They teach the immune system what a virus looks like. Then, when the body is attacked, it already knows how to fight the infection.
 
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　　Human bodies are very complex. And they are also very amazing! Scientists understand more about the human body every day. When people understand more about their bodies, they can make better choices about medicines. They may also have less fear of medicines like vaccines.
 
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　　The writer and producer of this program was Liz Waid. The voices you heard were from the United States and the United Kingdom. All quotes were adapted and voiced by Spotlight. You can find our programs on the internet at www.radioenglish.net. This program is called ‘How Vaccines Work’.
 
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　　We hope you can join us again for the next Spotlight program. Goodbye.