Preventing infection is better than treating it. A vaccine is a biological preparation that stimulates the immune system to recognize and defend against a specific infectious agent without causing the full disease.

Vaccines may contain weakened or killed organisms, purified antigens, toxoids, or nucleic acids that encode antigens. After vaccination the immune system produces antibodies and memory cells so that later exposure is met with a rapid, effective response. Schedules of primary doses and boosters optimize protection.

Vaccination has controlled or eliminated many once-common diseases. Safety monitoring systems detect rare adverse events. High coverage protects even unvaccinated individuals through herd immunity. Public confidence and reliable supply are as important as the science behind each vaccine.

• Preparation that induces protective immunity
• Uses antigens or genetic instructions without full disease
• Generates antibodies and immunological memory
• Underpins control of many infectious diseases