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Protection against a disease. Immunity may be indicated by the presence of antibodies in the blood, determined with a laboratory test. There are two types of immunity, active and passive.


When the immune system is unable to protect the body from disease. This condition can be caused by disease (like HIV infection or cancer) or by certain drugs (like those used in chemotherapy). Individuals whose immune systems are compromised should…

Incubation period

The time between when you come in contact with bacteria or viruses to when you start feeling sick.

Infectious agents

Organisms capable of causing disease (e.g., bacteria or viruses).

Investigational vaccine

A vaccine that has been approved by the Food and Drug Administration (FDA) for use in clinical testing in humans. However, investigational vaccines are still in the testing and evaluation phase and are not licensed for use in the general…


A type of bowel blockage that happens when one portion of the bowel slides into the next, much like the pieces of a telescope; it is treated in a hospital and may require surgery.


Influenza (more commonly known as the flu) is a highly contagious viral illness that is spread person-to-person through sneezes and coughs. It usually is a seasonal illness (October – May in the U.S.) and can be serious and life-threatening. One…


Redness, swelling, heat and pain in tissues (e.g., organs or muscles) resulting from injury or illness. Also known as swelling.


The number of new disease cases in a population over a certain period of time.

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