(a) What is a vaccine? How does a vaccine work? (b) Why are children given vaccination?

A vaccine is a biological preparation containing weakened, killed, or fragmented forms of disease-causing microorganisms (or their toxins) that stimulates the body's immune system to develop protection against specific infectious diseases without causing the actual illness. Vaccines work by introducing antigens—molecular components recognized as foreign by the immune system—which trigger the production of antibodies and activate immune memory cells without the risks associated with natural infection. When vaccinated, the immune system recognizes these antigens as threats, produces specific antibodies to neutralize them, and creates memory B and T cells that "remember" the pathogen for years or even a lifetime.

If the vaccinated person later encounters the actual pathogen, their immune system rapidly recognizes it and mounts a swift, powerful response by producing antibodies and activating immune cells before the pathogen can establish serious infection. This immunological memory provides immunity—the ability to resist infection or experience only mild symptoms if infected. Vaccines have proven extraordinarily effective, having eradicated smallpox globally, nearly eliminated polio, and dramatically reduced deaths from measles, diphtheria, tetanus, whooping cough, and numerous other diseases.

Children receive vaccinations because their immune systems are still developing and they are particularly vulnerable to serious complications and death from infectious diseases that adults might fight off more effectively. The first few years of life represent a critical window when children lose the passive immunity acquired from their mothers and before they develop their own robust immune responses through natural exposure. Childhood vaccination programs protect against diseases like measles, mumps, rubella, polio, diphtheria, tetanus, whooping cough, hepatitis B, rotavirus, and others that historically killed or disabled millions of children. Vaccinating children also creates herd immunity—when a large percentage of the population is immune, disease transmission becomes difficult, indirectly protecting those who cannot be vaccinated (infants too young, immunocompromised individuals). Early vaccination prevents suffering, saves lives, reduces healthcare costs, and enables healthy development into adulthood.