Vaccine: A substance or group of substances meant to cause the immune system to respond to a tumor or to microorganisms, such as bacteria or viruses.
Contagious: A disease which spreads from one person or organism to other, mainly by direct contact.
Virus: A simple pathogenic microorganism that invades living cells and uses cellular mechanisms to create multiple copies of itself.
Koplik’s spots: Little spots inside the mouth that are highly characteristic of the early phase of measles (rubeola).
Pneumonia: An inflammatory infection that occurs in the lung.
Encephalitis: Inflammation of the brain.