Immunity questions come every year in general science. Which cells fight germs? What is a vaccine? Who made the first vaccine? Which vitamin helps immunity? The answers do not change. This post explains immunity and vaccines in simple words, with a table of the vaccines exams ask about, followed by 15 previous year questions.
Key Points (Quick Revision)
- Immunity is the body's power to fight disease. White blood cells do this work.
- Innate immunity is present from birth. Acquired immunity is built after infection or a vaccine.
- Antigen is the germ or foreign thing. Antibody is the protein the body makes to fight it.
- Edward Jenner made the first vaccine, for smallpox, in 1796.
- BCG is for TB, OPV is polio drops, DPT covers three diseases.
1. What immunity means
Every day, germs enter our body through air, food and cuts in the skin. Most of the time we do not fall sick. The reason is immunity - the body's own system for finding and killing germs.
The main workers of this system are the white blood cells, also called leucocytes. They move around in the blood and the lymph. When a germ enters, they find it, attack it and remember it.
Two words are asked again and again:
- Antigen - any germ or foreign substance that enters the body. Bacteria, viruses, pollen, even a wrong blood group.
- Antibody - a protein made by the body to fight one particular antigen. Antibodies are made by B cells, a type of white blood cell.
One antibody works against one antigen only. That is why a person who had chickenpox once is safe from it later, but can still catch measles.
2. The two types of immunity
| Type | What it is | Example |
|---|---|---|
| Innate immunity | Present from birth. Works against all germs in the same way. | Skin, tears, mucus, stomach acid, fever, cells that eat germs |
| Acquired immunity | Built after meeting a germ or taking a vaccine. Works against one germ only. | Being safe from chickenpox after having it once |
Acquired immunity is split again into two, and this split is asked directly:
| Type | How you get it | How long it lasts |
|---|---|---|
| Active immunity | Your own body makes the antibodies - after an infection or a vaccine | Long, often for life |
| Passive immunity | Ready-made antibodies come from outside - from mother's milk, or an anti-serum injection (like anti-tetanus or anti-snake-venom) | Short, a few weeks or months |
The simple way to remember: vaccine = active (your body works), injection of ready antibodies = passive (someone else's antibodies work). A newborn baby gets passive immunity from the mother's first milk, called colostrum.
3. What a vaccine is and how it works
A vaccine is a weak or dead form of a germ, or a small part of it. It is given before a person falls sick. The body sees it as a real attack and makes antibodies. It also makes memory cells, which remember the germ for years.
When the real germ comes later, the body already knows it. It makes antibodies fast, and the person does not fall sick or gets only a mild illness. This is active immunity, made by the body itself.
Vaccines are made in a few ways, and the names are sometimes asked:
- Live weakened germ - BCG, oral polio drops, measles, MMR
- Killed germ - injectable polio (IPV), rabies, some flu vaccines
- Toxoid - a harmless form of the germ's poison, as in tetanus and diphtheria
- Part of the germ - hepatitis B, HPV
The study of vaccines is called vaccinology, and immunology is the study of the immune system as a whole.
4. People and dates that exams ask
| Name | Known for | Year |
|---|---|---|
| Edward Jenner | First vaccine, for smallpox; called the Father of Immunology | 1796 |
| Louis Pasteur | Rabies vaccine; also anthrax vaccine and pasteurisation | 1885 |
| Jonas Salk | Injectable polio vaccine (killed virus) | 1955 |
| Albert Sabin | Oral polio vaccine (drops) | 1961 |
| Calmette and Guerin | BCG vaccine for tuberculosis | 1921 |
Two facts from this table are near-certain questions. Jenner and smallpox - the first vaccine ever, and the word "vaccine" itself comes from vacca, the Latin word for cow, because Jenner used cowpox. And smallpox is the only human disease that has been fully wiped out from the world, declared by the WHO in 1980.
India was declared polio-free in 2014, and the Pulse Polio programme started in 1995. These two years are asked often.
5. Vaccines in India's immunisation programme
India gives free vaccines to children under the Universal Immunisation Programme (UIP), started in 1985. Mission Indradhanush, launched in 2014, was started to reach the children who were being missed. Learn the short forms and what each one covers.
| Vaccine | Protects against | Remember |
|---|---|---|
| BCG | Tuberculosis (TB) | Given at birth; leaves a small mark on the upper arm |
| OPV | Polio | Oral drops; the Pulse Polio drops |
| DPT | Diphtheria, Pertussis (whooping cough), Tetanus | Three diseases in one; now part of the Pentavalent vaccine |
| Pentavalent | DPT + Hepatitis B + Hib | Five in one |
| MMR | Measles, Mumps, Rubella | Three viral diseases |
| Rotavirus | Severe diarrhoea in infants | Oral |
| TT / Td | Tetanus | Given to pregnant women and after injuries |
| Covaxin / Covishield | COVID-19 | India's first COVID vaccines, 2021 |
Two of these are swapped in options most often. BCG is for TB, not for polio. And DPT covers three diseases, so any question that says "which vaccine covers diphtheria, whooping cough and tetanus" has DPT as the answer.
6. Other things that affect immunity
Vitamin C helps the body fight infection, and vitamin A keeps the skin and the lining of the nose and gut healthy - the body's first walls against germs. Zinc also helps.
The thymus gland is where T cells mature. It is large in children and shrinks with age, which is one reason older people fall sick more easily. The spleen and the lymph nodes store white blood cells and filter germs from the blood and lymph.
When the immune system attacks the body's own cells by mistake, it is called an autoimmune disease. Type 1 diabetes and rheumatoid arthritis are examples. When the immune system reacts too strongly to something harmless, like dust or pollen, it is called an allergy.
AIDS is a disease in which the HIV virus destroys the immune system itself, by attacking the T cells. The person then cannot fight even small infections.
7. Previous year questions
- Which cells in the blood fight germs? — White blood cells (leucocytes)
- What is the protein made by the body to fight a germ called? — Antibody
- Which cells make antibodies? — B cells (B lymphocytes)
- Who made the first vaccine? — Edward Jenner
- The first vaccine was made for which disease? — Smallpox
- Who is called the Father of Immunology? — Edward Jenner
- Who developed the rabies vaccine? — Louis Pasteur
- Who developed the oral polio vaccine? — Albert Sabin
- BCG vaccine protects against which disease? — Tuberculosis
- DPT vaccine protects against which three diseases? — Diphtheria, Pertussis and Tetanus
- Which is the only human disease to be fully wiped out from the world? — Smallpox, in 1980
- In which year was India declared polio-free? — 2014
- Immunity from the mother's milk is which type of immunity? — Passive immunity
- Which gland is the place where T cells mature? — Thymus
- In which year was the Universal Immunisation Programme started in India? — 1985
8. How to revise this topic
Start with the two pairs of words: antigen and antibody, and active and passive. If you can explain each pair in one line, half the chapter is done.
Then learn the five names - Jenner, Pasteur, Salk, Sabin, Calmette and Guerin - with one disease each. Jenner and smallpox is the one that comes most often.
Keep the vaccine table as short forms with one disease each. BCG for TB, OPV for polio, DPT for three, MMR for three. Read it twice a week.
Last, keep the years in one line: 1796, 1980, 1985, 1995, 2014. These five dates cover most of the date questions in this chapter.
9. Frequently Asked Questions
What is the difference between antigen and antibody?
An antigen is any germ or foreign thing that enters the body, like a virus or bacteria. An antibody is the protein the body makes to fight that one antigen. Antibodies are made by B cells, a type of white blood cell.
What is the difference between active and passive immunity?
In active immunity, your own body makes the antibodies, after an infection or a vaccine, and it lasts a long time. In passive immunity, ready-made antibodies come from outside, like from mother's milk or an anti-tetanus injection, and it lasts only a few weeks or months.
Who made the first vaccine and for which disease?
Edward Jenner made the first vaccine in 1796, for smallpox. He used cowpox, and the word vaccine comes from vacca, the Latin word for cow. He is called the Father of Immunology.
What does the DPT vaccine protect against?
Three diseases - diphtheria, pertussis (whooping cough) and tetanus. It is now given as part of the Pentavalent vaccine, which also covers hepatitis B and Hib.
Why does BCG leave a mark on the arm?
BCG is a live weakened vaccine against tuberculosis, given at birth on the upper arm. The body reacts to it with a small sore that heals into a scar. The scar is normal and shows the vaccine was given.
For more General Science topics in simple language, see our Human Diseases and Blood Groups and Human Blood posts, or browse the General Science section. Preparing for a specific exam? Start with the SSC CGL guide or join the 100 Hour GS Course.