Two Accidents That Saved Billions of Lives

According to the World Health Organization, health is defined as a state of complete physical, mental and social well-being, and not merely the absence of disease. A healthy person can generally perform tasks more efficiently, cope well in difficult situations, and adjust well with peer groups and other members of society; being happy helps a person stay active and healthy, and good health in turn improves mood, so health and happiness are closely linked. A student who moves to a new school, has no friends, and feels increasingly lonely can develop headaches, lose weight and sleep poorly, even without any infection at all, purely from the absence of social and mental well-being; this is exactly the kind of case the WHO definition is built to capture, since health clearly depends on more than just physical symptoms alone.

Staying healthy depends on both lifestyle, how a person lives, and environment, the surroundings a person lives in. On the lifestyle side, eating a balanced diet with plenty of fruits, vegetables and whole grains, avoiding processed and sugary food, staying physically active, limiting screen time, getting enough sleep, and saying no to harmful substances like tobacco and alcohol all support health directly. On the environment side, a clean, well-maintained space is healthier to live and play in than a polluted, unhygienic one full of flies and mosquitoes; clean air and water matter too, since air pollution from vehicles and factories can cause coughing or asthma, tracked using the Air Quality Index. But health is not only about the body: feelings and relationships matter as well, since even a person who eats well and lives in a clean place may not feel good if lonely or upset, which is exactly why spending time with friends and family, talking, laughing and having fun genuinely helps keep the mind healthy too.

A disease is a condition that affects the normal working of the body or mind, and can be grouped into two major types. Communicable diseases are caused by pathogens, disease-causing organisms like bacteria, viruses, fungi, worms or protozoa, and can spread from one person to another; typhoid, dengue, flu, chickenpox and COVID-19 are all examples. Non-communicable diseases, like cancer, diabetes and asthma, are not caused by pathogens at all and don't spread between people; they're usually linked to lifestyle, diet or environment instead. In recent years, non-communicable diseases have become more common in India due to changes in how people live, more processed food, less exercise, longer lifespans, and today, most deaths in India are actually caused by NCDs rather than infectious disease. Pathogens spread from an infected person through several routes: through the air when someone coughs or sneezes, through direct contact like shaking hands, indirectly by sharing personal items, through contaminated food or water, and through vectors, insects like mosquitoes and houseflies that carry pathogens from one host to another.

Understanding exactly how communicable diseases spread makes them far easier to prevent. Diseases spread through the air include common cold and influenza (nasal congestion, sore throat, fever), chickenpox (itchy skin rashes and blisters), measles (fever and reddish rashes) and tuberculosis (cough, fatigue, night sweats), each preventable through handwashing, not sharing personal items, covering the mouth and nose, and in several cases, vaccination. Diseases spread through contaminated water and food include hepatitis A (jaundice, nausea), cholera (diarrhoea and dehydration), typhoid (fever and abdominal discomfort) and ascariasis, a roundworm infection causing poor growth and anaemia, all preventable through good sanitation, properly cooked food and boiled drinking water. Diseases transmitted by insect vectors include malaria (high fever, chills, spread by mosquitoes) and dengue fever (fever, joint pain, also mosquito-spread), preventable through mosquito nets, repellents and controlling mosquito breeding sites. Simple, shared precautions run through almost every category: keeping ourselves and our surroundings clean, washing hands with soap, covering the mouth and nose while coughing or sneezing, avoiding sharing personal items, and staying home to rest when unwell, which helps the body recover while minimising spread to others.

Non-communicable diseases like cancer, diabetes and asthma are linked to lifestyle, diet and environment, and are the most common cause of death in India today; when they persist for a long time, more than three months, they're referred to as chronic diseases. Deficiency diseases like scurvy, anaemia and goitre, caused by a lack of specific nutrients in the diet, also fall under this non-communicable category, since they aren't caused by any pathogen either. Diabetes, one of the most common non-communicable diseases and increasingly prevalent in both adults and children in India, often develops due to a combination of hormonal imbalances, unhealthy eating habits, lack of physical activity, and being overweight or obese. Managing non-communicable diseases relies on a different approach than treating an infection: therapies focus on managing symptoms and improving quality of life through medication, lifestyle changes and rehabilitation, with early diagnosis and continuous care key to controlling how the disease progresses and preventing complications.

The natural ability of the body to fight disease is called immunity, carried out by a special immune system. Smallpox was once a deadly disease, causing blisters and killing millions; a much milder disease called cowpox, seen in cows, could also infect humans. In the late 1700s, English doctor Edward Jenner observed that milkmaids who had caught cowpox did not go on to get smallpox, and hypothesised that something in the pus of cowpox blisters protected people from smallpox. He tested this by injecting cowpox sap into a boy, who later showed no illness when deliberately exposed to smallpox; mass vaccination based on this discovery eventually helped eradicate smallpox worldwide, with the last natural case recorded in 1979. A vaccine works by training the immune system to recognise and attack a harmful germ, providing what's called acquired immunity, protection developed after exposure to a pathogen or a vaccine; vaccines can be made from weakened or dead pathogens, from harmless parts of a pathogen, or, in newer methods, by instructing the body's own cells to make a harmless part of the germ for the immune system to learn from. Vaccines are preventive, not curative, meaning they help minimise disease before it happens but don't treat someone already sick, and getting vaccinated protects the people around a person as well as the person themselves. Long before Jenner, India already had a traditional method called variolation, using material from a smallpox sore to create a mild infection and build immunity, practised by people known as teekedaars.

When the immune system fails to protect against an infection, a doctor may prescribe antibiotics, medicines that kill the bacteria causing the disease. Antibiotics work only against bacterial infections, because they target parts of bacterial cells that are different from human or other animal cells; they don't work against viruses or diseases caused by protozoa at all. Penicillin, the first antibiotic, was discovered in 1928 by Alexander Fleming, a London bacteriologist studying harmful bacteria, who noticed that a mould accidentally growing on a discarded petri dish had stopped the bacteria around it from growing; he realised the mould was releasing a substance that killed the bacteria, a chance discovery that led directly to the first antibiotic used to treat bacterial infections. Though antibiotics have saved millions of lives since their discovery, indiscriminate use has led to a decline in their effectiveness, a phenomenon called antibiotic resistance, where bacteria once killed by a given antibiotic survive and multiply despite treatment with it. This happens because a few bacteria naturally resist a given antibiotic; when antibiotics kill off the susceptible bacteria around them, including helpful bacteria that protect the body, the resistant bacteria grow and take over, and can even transfer their resistance to other bacteria, spreading the problem further through communities, animals, and hospitals alike. Using antibiotics wisely, only when prescribed, at the correct dose, for the right duration, and never for viral infections like a cold or flu, is essential to slow this down and keep antibiotics effective for the future.

In Bhadrak district, Odisha, a community-led sanitation campaign that helped more people build and use toilets significantly reduced open defecation and improved child health, with fewer cases of diarrhoea and infection, a clear demonstration that simple steps like good sanitation can greatly reduce the spread of communicable disease. Traditional medicine systems like Ayurveda, Siddha and Unani have long been used in India to manage common health problems using natural substances and a focus on healthy lifestyle and balanced diet; they can help with some conditions and everyday well-being, though they may not be effective for all diseases at all stages. Between good sanitation, vaccination, wise antibiotic use, and a healthy lifestyle addressing both communicable and non-communicable risk, the overall message of this chapter comes together clearly: prevention is better than cure, and it is achievable through fairly ordinary, well-understood actions rather than anything exotic.