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How do vaccines protect us from diseases?

Class 8 ScienceNCERT chapter: The Invisible Living World: Beyond Our Naked Eyeइसे हिंदी में पढ़ें

Exam-ready answer

A vaccine contains dead or weakened disease-causing microbes, or parts of them. When it is given, the body treats them as invaders and produces antibodies to fight them. The body also remembers this microbe. If the real microbe enters later, the body makes antibodies quickly and destroys it before it can cause the disease.

Explanation

When disease-causing microbes, called pathogens, enter our body, the body's defence system produces special proteins called antibodies. Antibodies attach to the microbes and help destroy them. The first time this happens, the body takes time to make enough antibodies, and during that time we may fall ill.

A vaccine uses this natural defence safely. It contains microbes that are dead or weakened so that they cannot cause the illness, or only parts of them. The body still recognises them as foreign and makes antibodies. Importantly, the body keeps a memory of that particular microbe. This process of giving a vaccine is called vaccination or immunisation.

Later, if the real microbe enters, the body recognises it at once and produces antibodies quickly in large numbers. The microbe is destroyed before it can multiply and make us sick. Vaccines are available for diseases such as polio, measles, tuberculosis and tetanus. When most people in a community are vaccinated, the disease also finds it harder to spread to others.

Points to remember

Vaccine: a preparation of dead or weakened microbes (or their parts) that gives protection against a disease.
Antibodies: proteins made by the body that help destroy specific invading microbes.
The body remembers the microbe after vaccination and responds faster the next time.
Vaccination (immunisation) protects against diseases like polio, measles, tuberculosis and tetanus.
Each vaccine protects against a specific disease, not against all diseases.

Exam tip

Use the key words 'dead or weakened microbes', 'antibodies' and 'memory' in your answer, and write the steps in order: vaccine enters, antibodies form, body remembers, real infection is stopped.

Questions students also ask

Can a vaccine cause the disease it protects against?

Vaccines are made from dead or weakened microbes, or their parts, which cannot cause the full disease in healthy people. A mild fever or soreness may occur as the body responds. Any concerns should be discussed with a doctor.

Why are some vaccines given more than once?

For some diseases, one dose does not build strong or long-lasting memory in the body. Extra doses, called booster doses, strengthen the body's response so the protection lasts longer.

What is the difference between a vaccine and an antibiotic?

A vaccine is given before infection to prepare the body to fight a particular disease. An antibiotic is a medicine given after a bacterial infection to kill or stop the growth of bacteria.

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