Human Diseases and Vaccines Notes for UPSC

Health is a regular part of the Science and Technology section of the UPSC Civil Services Examination. Questions come from communicable and non-communicable diseases, their causes, vaccines, antibiotic resistance and public health programmes, and they are often linked with news such as outbreaks, new vaccines and WHO announcements. The COVID-19 pandemic made this topic even more important. This note explains human diseases and vaccines in simple language, with tables and Indian programmes, so that you can answer both Prelims and Mains questions.

Classification of Human Diseases

Diseases are mainly divided into two groups. Communicable (infectious) diseases spread from one person to another through germs (pathogens) such as bacteria, viruses, fungi, protozoa and worms. Non-communicable diseases (NCDs) do not spread from person to person; they are caused by lifestyle, genes, environment and ageing, and include diabetes, heart disease, cancer, stroke and chronic lung disease. NCDs now cause the majority of deaths in India, while infectious diseases still remain a major burden. Diseases can also be congenital (present from birth), deficiency diseases (due to lack of a nutrient) and genetic or hereditary diseases.

Communicable Diseases by Pathogen

Important vector-borne diseases: dengue and chikungunya (Aedes mosquito), malaria (Anopheles), Japanese encephalitis (Culex), and kala-azar (sandfly). Diseases transmitted by contaminated water and food include cholera, typhoid, hepatitis A and diarrhoea. Air-borne diseases include tuberculosis, influenza, measles and COVID-19.

Key Diseases in Detail

Tuberculosis (TB) is caused by Mycobacterium tuberculosis and mainly affects the lungs. India has the highest TB burden in the world, and the government aims to eliminate TB by 2025 under the National TB Elimination Programme, five years ahead of the global goal; the BCG vaccine is given to infants, and treatment uses a combination of drugs under DOTS. Malaria is caused by the Plasmodium parasite and shows fever with chills. HIV/AIDS is caused by the Human Immunodeficiency Virus, which attacks the CD4 T-cells of the immune system; it spreads through unprotected sex, blood, infected needles and from mother to child, but not by touching or sharing food. Hepatitis B and C damage the liver. Dengue causes high fever and a fall in platelets. Polio was eliminated from India (certified in 2014), and smallpox was declared eradicated worldwide in 1980, the only human disease eradicated so far, followed by the animal disease rinderpest in 2011.

Non-Communicable Diseases

Diabetes arises when the body cannot make or use insulin properly; Type 1 is due to lack of insulin and Type 2 is linked to lifestyle. Hypertension (high blood pressure) is a major cause of heart attack and stroke. Cancer is uncontrolled growth of cells; risk factors include tobacco, alcohol, pollution and infection by viruses like HPV. Cardiovascular diseases are the leading cause of death. Prevention depends on healthy food, exercise, avoiding tobacco and alcohol, regular screening and the early treatment of high blood pressure and sugar. The National Programme for Prevention and Control of Non-Communicable Diseases and the Ayushman Bharat Health and Wellness Centres focus on screening.

Deficiency Diseases

• Vitamin A: night blindness. Vitamin B1: beriberi. Vitamin C: scurvy. Vitamin D: rickets. Vitamin K: poor blood clotting.
• Iron: anaemia. Iodine: goitre. Protein: kwashiorkor and marasmus.

Immunity and Vaccines

Immunity is the body's ability to fight germs. Innate immunity is present from birth (skin, mucus, white blood cells). Acquired immunity develops after infection or vaccination. A vaccine contains a weakened, killed or partial form of a germ, or its genetic instructions, so that the body learns to make antibodies without getting the disease, and remembers it for the future. This creates active immunity. Passive immunity comes by giving ready-made antibodies, as in mother's milk or anti-snake venom. Edward Jenner developed the first vaccine for smallpox in 1796, and Louis Pasteur made vaccines for rabies and anthrax. When a large share of the population is immune, even the unvaccinated are protected; this is herd immunity.

Types of Vaccines

Live attenuated vaccines use a weakened germ (measles, oral polio, BCG). Inactivated vaccines use a killed germ (injectable polio, Covaxin). Subunit or toxoid vaccines use only a part or a toxin (hepatitis B, tetanus, diphtheria). Viral vector vaccines use a harmless virus to carry a gene (Covishield). mRNA vaccines give the instructions to make a protein of the virus and were first widely used for COVID-19. India also developed an indigenous DNA vaccine (ZyCoV-D) and the HPV vaccine Cervavac for cervical cancer.

Immunisation and Health Programmes in India

The Universal Immunisation Programme (UIP) provides free vaccines against more than ten diseases, including TB, polio, hepatitis B, diphtheria, pertussis, tetanus, measles, rubella and rotavirus diarrhoea. Mission Indradhanush and Intensified Mission Indradhanush reach children and pregnant women who were missed. The U-WIN portal digitises vaccination records. The COVID-19 vaccination drive, supported by the CoWIN platform, gave over 2 billion doses. India produces a large share of the world's vaccines, which earned it the title "pharmacy of the world".

Antimicrobial Resistance (AMR)

When germs learn to survive medicines, the drugs stop working; this is antimicrobial resistance, and it is a growing global threat. Causes are over-use and wrong use of antibiotics, taking antibiotics for viral infections, incomplete courses, use in animal farming and poor hygiene. A resistant germ is called a superbug. India has a National Action Plan on AMR, and the Red Line campaign asks people to buy antibiotics only on a doctor's prescription. Remedies include the careful use of drugs, infection control, new drug research and the "One Health" approach, which links human, animal and environmental health.

Epidemic, Pandemic and Related Terms

Several words are used when we talk about outbreaks. An endemic disease is always present in a particular area, like malaria in some parts of India. An epidemic is a sudden rise in the number of cases in an area. A pandemic is an epidemic that spreads across many countries and continents, as COVID-19 did. An outbreak is a small, local epidemic. A zoonotic disease jumps from animals to humans, for example rabies, Nipah, bird flu and COVID-19. A vector is an organism, such as a mosquito, that carries a germ from one host to another. A carrier is a person who has the germ and can spread it without showing symptoms. The World Health Organization (WHO), headquartered in Geneva, declares a Public Health Emergency of International Concern for serious events, and India follows the International Health Regulations. Knowing these words helps you decode the meaning of many news headlines.

Public Health Strategy: Prevention Is Better Than Cure

A good health system works at three levels. At the first level, primary prevention stops disease before it starts, through clean water, sanitation, nutrition, vaccines and health education. At the second level, early detection through screening finds disease when it is easy to treat. At the third level, treatment and rehabilitation reduce the damage. India's schemes such as the National Health Mission, Ayushman Bharat (PM-JAY, which gives health cover of up to 5 lakh rupees per family), the Swachh Bharat Mission and the Poshan Abhiyaan work across these levels. A short Mains answer should state that health is a shared responsibility of the state, the community and the individual, and should add the idea of One Health, which treats human, animal and environmental health as one system. Also say that strong primary health centres, trained health workers and affordable medicines are the real base for controlling both infectious and lifestyle diseases.

Important Diseases in the News

Keep short notes on diseases that often appear in current affairs: Nipah virus (spread from bats, seen in Kerala), Zika (Aedes mosquito), bird flu (avian influenza), African swine fever, mpox, monkeypox-like outbreaks, Kyasanur Forest Disease (ticks, in Karnataka) and the rise of drug-resistant TB. For each one, note the pathogen, the way it spreads, the region and the response. This habit turns a long list into a quick and reliable revision sheet.

Quick Revision

• Smallpox is the only human disease eradicated (1980); polio-free India certified in 2014.
• TB: Mycobacterium; BCG vaccine; India has the highest burden.
• Malaria: Plasmodium; Anopheles. Dengue: Aedes. HIV attacks CD4 cells.
• UIP and Mission Indradhanush deliver free vaccines. AMR: superbugs.

Health topics are easy to score if you build a good table of disease, pathogen, vector and prevention. Add the latest national programmes and WHO news, and you will be ready for any question on diseases and vaccines.

Related Notes to Read Next

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Frequently Asked Questions (FAQ)

What are communicable diseases?

Communicable diseases are infectious diseases that spread from one person to another through germs such as viruses, bacteria, fungi and parasites.

What is the difference between communicable and non-communicable diseases?

Communicable diseases spread between people through pathogens, while non-communicable diseases such as diabetes and heart disease do not spread and are caused by lifestyle, genes and environment.

How does a vaccine work?

A vaccine introduces a harmless form of a germ or its instructions into the body so the immune system learns to recognise it and responds quickly if the real germ enters later.

What is herd immunity?

Herd immunity occurs when a large part of a population becomes immune to a disease, which reduces its spread and protects even those who are not immune.

Which disease has been eradicated worldwide?

Smallpox was declared eradicated in 1980. It is the only human disease eradicated so far.

What is the Universal Immunisation Programme?

The UIP is the Government of India programme that provides free vaccination to children and pregnant women against several vaccine-preventable diseases.

What is Mission Indradhanush?

It is a government immunisation mission launched in 2014 to reach children and pregnant women who have missed their routine vaccines.

Which mosquito spreads malaria and dengue?

Malaria is spread by the female Anopheles mosquito, and dengue is spread by the Aedes mosquito.

What is antimicrobial resistance?

It is the ability of germs to survive the drugs that once killed them, making infections hard to treat. It is caused mainly by misuse of antibiotics.

What is an mRNA vaccine?

An mRNA vaccine gives the body a set of instructions to make a harmless piece of a virus protein, which trains the immune system without using the live virus.

What causes tuberculosis?

TB is caused by the bacterium Mycobacterium tuberculosis and mainly spreads through the air when an infected person coughs.

What is the BCG vaccine?

BCG is a vaccine given to infants to protect against severe forms of tuberculosis.