What is a vaccine?

A vaccine is a biological preparation that trains the immune system to recognise and fight a specific pathogen without causing actual disease.

• Introduces a harmless antigen → immune system creates antibodies + memory cells.
• If real pathogen invades later → rapid, powerful immune response.

Examples: Polio vaccine, MMR, COVID-19 vaccine.

Vaccines have eradicated smallpox and nearly eliminated polio globally.

A vaccine stimulates the immune system to create memory cells against a pathogen, providing protection without causing disease.