A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and recognize further and destroy any of the microorganisms associated with that agent that it may encounter in the future.

ಲಸಿಕೆ ಎಂದರೆ ಸೂಕ್ಷ್ಮಜೀವಿ ಅಥವಾ ವೈರಸ್‍ಗಳನ್ನು ಕೊಂದು ಇಲ್ಲವೇ ದುರ್ಬಲೀಕರಿಸಿ ತಯಾರಿಸಿದ ದ್ರವಪದಾರ್ಥ (ವ್ಯಾಕ್ಸಿನ್). ಇದನ್ನು ಚುಚ್ಚುಮದ್ದಾಗಿ ರಕ್ತಪರಿಚಲನ ವ್ಯವಸ್ಥೆಗೆ ಹೊಗಿಸಿದಾಗ ಅದರಲ್ಲಿ ಪ್ರತಿಕಾಯಗಳು ಜನಿಸಿ ವ್ಯಕ್ತಿಗೆ ಆಯಾ ರೋಗದ ಎದುರು ರಕ್ಷೆ ಒದಗಿಸುತ್ತವೆ.