ScienceCBSE Class 8 · Health: The Ultimate Treasure

Immunity, Vaccines and Antibiotics: Class 8 Science

Updated 17 October 2026 · Fact-checked

Immunity is the natural ability of the body to fight disease. Vaccines train the immune system to recognise a germ and give acquired immunity; they prevent but do not cure. Antibiotics kill bacteria only, so they do not work against viruses, and wrong use makes bacteria resistant.

A vaccine prevents disease by training immunity, while an antibiotic only kills bacteria, never viruses, and wrong use makes bacteria resistant.

Illustration drawn for QuestionBuddy.

Understand Immunity, Vaccines and Antibiotics

Immunity. Some people fall sick more often than others living in the same surroundings. The natural ability of the body to fight diseases is immunity, and the immune system is the special system that does this. Protection developed after exposure to a pathogen or after a vaccine is acquired immunity. The chapter's question 11 points out that on a second exposure to the same pathogen the response is much stronger than on the first.

Vaccines. Drops or injections given in childhood against polio, measles, tetanus and hepatitis are vaccines. A vaccine trains the immune system to recognise and attack harmful germs. Vaccines can be made from weakened or dead pathogens, or from inactive or harmless parts of a pathogen; some newer vaccines instruct our own cells to make a harmless part of the germ. A tetanus shot contains an inactivated bacterial toxin, so the body learns to protect itself without the disease. Vaccines are preventive, not curative: they help minimise serious disease before it happens but do not treat someone already sick. They are carefully tested for safety, and vaccination protects the people around us too.

Jenner and smallpox. Smallpox was a deadly disease that caused blisters. In the late 1700s the English doctor Edward Jenner observed that milkmaids who had cowpox did not catch smallpox (observation); he guessed that the pus of cowpox blisters protected people (hypothesis); he tested it by injecting cowpox sap into a boy, who stayed well when exposed to smallpox (experiment); people were resistant (result); mass vaccination later eradicated smallpox. According to the chapter's graph a vaccine campaign began in 1965 and smallpox was eradicated in 1979. The heritage note adds that India had variolation, performed by teekedaars. India is one of the world's largest vaccine producers.

Antibiotics. Doctors give antibiotics for bacterial infections. They kill bacteria by targeting parts of bacterial cells that differ from human and animal cells, so they do not work against viruses (cold, cough, flu) or protozoa (malaria). Penicillin, the first antibiotic, was discovered in 1928 by Alexander Fleming, who noticed that a mould on a discarded petri dish stopped bacteria growing.

Antibiotic resistance. If antibiotics are taken when they are not needed, or the dose is left incomplete, some bacteria survive, multiply and pass on resistance to others. Then the same antibiotic no longer kills them, infections become harder to treat and complications, longer illness and death are more likely. Use antibiotics only when a doctor prescribes them, in the right dose and for the right duration. Resistance can also spread through animals, manure, crop produce and hospitals.

Treatment of NCDs. Therapies focus on managing symptoms and improving quality of life by medicines, lifestyle changes and rehabilitation; early diagnosis and continuous care matter. Traditional systems (Ayurveda, Siddha, Unani) use herbs, oils and minerals and a healthy lifestyle, but may not be effective for all diseases at all stages.

The previous topic gave types of diseases and how they spread.

Immunity, Vaccines and Antibiotics: formulas and key facts

Immunity: $N a t u r a l abi l i t y o f t h e b o d y t o f i g h t d i se a se ∣ A c q u i r e d imm u ni t y = a f t er a p a t h o g e n or a v a cc in e$; The immune system carries it out.
Types of vaccine material: Weakened pathogen
Dead pathogen
Inactive or harmless part
Instructions for cells to make a harmless part; Tetanus shot uses an inactivated toxin.
Jenner's steps: $O b ser v a t i o n > H y p o t h es i s > E x p er im e n t > R es u l t > A ppl i c a t i o n$; Late 1700s; smallpox eradicated by 1979.
Antibiotic scope: $B a c t er ia : y es ∣ V i r u ses : n o ∣ P r o t oz o a : n o$; Penicillin discovered by Fleming in 1928.
Wise use of antibiotics: Only when prescribed
Correct dose
Right duration; Avoids resistance.

How to solve Immunity, Vaccines and Antibiotics questions

Use this method for questions on prevention and treatment.

1Decide the type of pathogen (bacteria, virus, protozoa).
2If the question is about prevention, think of vaccines and hygiene; if cure, think of the doctor, medicine and antibiotics (bacteria only).
3For vaccines, say that they prepare the immune system and are preventive, not curative.
4For resistance, give the cause (unnecessary or incomplete use) and the effect (harder to treat).
5For history questions, give the scientist, the observation and the result.
6End with a precaution.

Immunity, Vaccines and Antibiotics in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Vaccination coverage

Suppose a school of 800 students holds a vaccination drive in which 664 students are vaccinated against a bacterial disease (made-up numbers).

(a) What percentage of students are vaccinated? (b) How many are not? (c) A student says that the vaccine will cure a classmate who already has the disease. Reply. (d) Why does a high vaccination rate also help students who are not vaccinated?

Try it first, then show the solutionSolution

664 ÷ 800 × 100 = 83%.
800 − 664 = 136 students.
Vaccines are preventive, not curative; they do not treat someone already sick.
Fewer people carry and pass on the pathogen, so the spread is reduced and others are better protected.

Answer: (a) 83%; (b) 136; (c) vaccines prevent, not cure; (d) less spread of the infection.

Memory hook: A vaccine is a practice test before the real exam.

Misuse of antibiotics

Imagine Ravi has a cold and takes leftover antibiotic tablets for 2 days of a 5-day course for a different illness, then stops.

(a) Why are antibiotics not suitable for a cold? (b) What risk did Ravi create by stopping early? (c) How many days of the 5-day course did he skip, as a percentage? (d) State the right practice.

Try it first, then show the solutionSolution

A cold is caused by a virus; antibiotics work only against bacteria.
Some bacteria may survive, multiply and become resistant.
Skipped = 5 − 2 = 3 days; 3 ÷ 5 × 100 = 60%.
Use antibiotics only when prescribed by a doctor, in the correct dose and for the right duration.

Answer: (a) Virus, not bacteria; (b) resistance; (c) 60%; (d) only as prescribed.

Memory hook: Right drug, right dose, right days, right doctor.

Tricks to remember Immunity, Vaccines and Antibiotics

Short memory aids. Say each one aloud once, then use it on a question the same day.

Vaccine = prevent, Antibiotic = treat bacteria
V for 'Venture ahead' (prevention), A for 'Attack bacteria' (treatment).
Use it when: Distinguishing the two.
OHERA for Jenner
Observation, Hypothesis, Experiment, Result, Application.
Use it when: Jenner case study.
Antibiotics bypass viruses
Cold, cough, flu = virus = no antibiotic.
Use it when: Application questions.

Immunity, Vaccines and Antibiotics: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Vaccines: prevention not cure · 2 marks · Short answerBoard level

Explain how a vaccine protects us and why it is called preventive and not curative.

Try it first, then show the solutionSolution

A vaccine trains the immune system to recognise and attack a particular germ, giving acquired immunity. (1)
It helps prevent a serious disease before it happens, but does not treat a person who is already sick. (1)

Answer: A vaccine trains the immune system in advance; it prevents but does not cure.

Example 2: Who discovered penicillin · 1 mark · MCQBoard level

The first antibiotic, penicillin, was discovered in 1928 by
(a) Edward Jenner
(b) Alexander Fleming
(c) Kamal Ranadive
(d) Robert Hooke

Try it first, then show the solutionSolution

Fleming noticed that a mould on a discarded petri dish stopped bacteria growing.

Answer: (b)

Example 3: Antibiotic resistance explained · 5 marks · Long answerHarder board level

(a) What is meant by antibiotic resistance? (1) (b) Give two ways in which resistance develops. (2) (c) Why should antibiotics not be used for a viral cold? (1) (d) Give two precautions. (1)

Try it first, then show the solutionSolution

(a) Bacteria that were earlier killed by an antibiotic now survive and multiply despite the treatment. (1)
(b) Taking antibiotics when not required; taking incomplete doses; also use in animals. (2)
(c) A cold is caused by a virus; antibiotics target parts of bacterial cells that viruses do not have, so they do not work. (1)
(d) Take them only when a doctor prescribes, in the correct dose for the right duration. (1)

Answer: Resistance is survival and multiplication of bacteria despite treatment; caused by unnecessary use or incomplete doses; antibiotics do not work on viruses; use only when prescribed.

Example 4: Jenner as an investigation · 4 marks · Case-basedHarder board level

Read the passage and answer.

In the late 1700s Jenner noticed that milkmaids who had had cowpox did not catch smallpox. He suspected that the matter in cowpox blisters protected people. He injected cowpox sap into a boy, who later showed no illness when exposed to smallpox.
(a) State his observation and his hypothesis. (1)
(b) What was the experiment? (1)
(c) What did the result suggest? (1)
(d) Was the later eradication of smallpox due to vaccination or to a cure for those already sick? Explain. (1)

Try it first, then show the solutionSolution

(a) Observation: milkmaids with cowpox did not get smallpox. Hypothesis: content of cowpox blisters protects from smallpox. (1)
(b) He injected cowpox sap into a boy and exposed him to smallpox. (1)
(c) People infected with cowpox sap were resistant to smallpox. (1)
(d) By mass vaccination, which prevents disease; it was not a cure for the sick. (1)

Answer: (a) Milkmaids safe; cowpox pus protects; (b) injection of cowpox sap; (c) resistance to smallpox; (d) vaccination (prevention).

Example 5: Immune response on repeat exposure · 4 marks · Case-basedHOTS / competency

Read the passage and answer.

When a body meets a pathogen for the first time, the immune response is generally low. On meeting it again the response is much stronger. A health worker says: 'This is the reason for a vaccine, and also the reason some people avoid the same infection twice.' Another says: 'A vaccine can replace antibiotics for all infections.'
(a) Suggest why the second response is stronger. (1)
(b) How does this idea support vaccination? (1)
(c) Evaluate the second statement. (1)
(d) A doctor prescribes an antibiotic for tuberculosis. Say why a vaccine is also used for it. (1)

Try it first, then show the solutionSolution

(a) The immune system has already been trained to recognise the pathogen and responds faster and more strongly. (1)
(b) A vaccine gives this training safely, using weakened, dead or harmless parts of the germ. (1)
(c) Wrong: vaccines prevent disease; antibiotics treat bacterial infection; they do different jobs and neither works on every pathogen. (1)
(d) The antibiotic treats the infection; the vaccine helps prevent the disease (the chapter lists vaccination among the preventive measures for TB). (1)

Answer: (a) Trained immune system; (b) safe training; (c) not correct, different jobs; (d) prevention plus treatment.

Where students lose marks in Immunity, Vaccines and Antibiotics

The slips examiners see most often, and what to write instead.

Mistake: Saying vaccines cure diseases.
Vaccines are linked with medicine in general.
Wrong working
A vaccine cures a person who is ill.
Right working
A vaccine prevents disease by preparing the immune system; it does not treat a person already sick.
Do this: Use 'preventive, not curative'.
Usually costs: 1 mark.
Mistake: Stating that antibiotics work against viruses.
Antibiotics are the best known medicine.
Wrong working
Take an antibiotic for flu.
Right working
Antibiotics act only on bacteria; flu is caused by a virus.
Do this: Check the pathogen first.
Usually costs: 1 to 2 marks.
Mistake: Mixing the names of scientists.
Several names appear in the chapter.
Wrong working
Fleming discovered the smallpox vaccine.
Right working
Jenner: smallpox vaccine (late 1700s). Fleming: penicillin (1928).
Do this: Jenner = Jab; Fleming = Fungus (mould).
Usually costs: 1 mark.
Mistake: Defining resistance as the body becoming resistant.
Resistance is confused with immunity.
Wrong working
Antibiotic resistance means the body resists antibiotics.
Right working
The bacteria become resistant: they survive and multiply despite the antibiotic.
Do this: The word 'bacteria' must appear.
Usually costs: 1 mark.

Exam tips

Give 'prevent' with vaccines and 'treat bacterial infection' with antibiotics.
For history questions use dates and names exactly as in the chapter: Jenner, late 1700s; Fleming, 1928.
In resistance answers include cause, effect and precaution.
Avoid saying vaccines are 100 per cent safe or risky; say they are carefully tested.
In percentage problems show division, multiplication by 100 and the unit.

Practice questions on Immunity, Vaccines and Antibiotics

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 2 marks · Very short answerBoard level
Define immunity and name the system responsible.
Hint
Natural ability of the body.
Answer
Immunity is the natural ability of the body to fight diseases (1); the immune system does this (1).
Q2 · 1 mark · MCQBoard level
Antibiotics are effective against
(a) viruses only
(b) protozoa only
(c) bacteria only
(d) all pathogens
Hint
They target parts of bacterial cells.
Answer
(c)
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): A person should not stop an antibiotic course early.
Reason (R): Bacteria that survive an incomplete dose can multiply and become resistant.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Think of the effect of survivors.
Answer
(a) R explains why the course must be completed.
Q4 · 4 marks · Short answerHarder board level
A town of 12 500 people runs a vaccination drive and 10 000 are vaccinated. (a) Find the percentage vaccinated. (b) How many are unvaccinated? (c) Each group visit takes 40 people; how many whole visits are needed to vaccinate the remaining people? (d) Name one reason this protects the unvaccinated.
Hint
Divide, then round up for visits.
Answer
(a) 10 000 ÷ 12 500 × 100 = 80%. (b) 2 500. (c) 2 500 ÷ 40 = 62.5, so 63 visits. (d) Less spread of the pathogen (1 mark each).
Q5 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
Saniya says: 'Antibiotics can cure any infection, so we need not worry about disease.' Vinita wants to help her see the mistake. A flu patient asks for antibiotics.
(a) Write two questions Vinita can ask. (b) Why do antibiotics fail against flu? (c) What is antibiotic resistance? (d) Name two actions that reduce it.
Hint
Think of the pathogen groups and misuse.
Answer
(a) For example: Do antibiotics work against viruses? What happens if bacteria survive an incomplete course? (b) Flu is caused by a virus and antibiotics act only on bacteria. (c) Bacteria that survive and multiply despite the antibiotic that once killed them. (d) Use only when prescribed, in the right dose and for the right duration (1 mark each).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is acquired immunity?Show answer
Protection developed after exposure to a pathogen or after a vaccine.
2.Who discovered the first vaccine?Show answer
Edward Jenner, for smallpox, in the late 1700s.
3.Who discovered penicillin and when?Show answer
Alexander Fleming, in 1928.
4.Why do antibiotics not work against viruses?Show answer
They target parts of bacterial cells that are different from human cells and are not in viruses.
5.Are vaccines preventive or curative?Show answer
Preventive.
6.Who were the teekedaars?Show answer
People who performed variolation, the traditional Indian method against smallpox.

Immunity, Vaccines and Antibiotics: frequently asked questions

How is a vaccine made?

From weakened or dead pathogens, from inactive or harmless parts of them, or, in newer vaccines, from instructions that make our own cells produce a harmless part of the germ.

Why are some people sick more often?

The chapter says the natural ability to fight disease, immunity, differs between people even in similar surroundings.

Can I stop an antibiotic once I feel better?

Antibiotics should be used in the correct dose and for the right duration as prescribed, because incomplete use can encourage resistance.

Do traditional medicines replace modern ones?

The chapter says traditional systems help with some conditions and everyday well-being, but may not be effective for all diseases and at all stages.