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Vaccines work by triggering a response by the body’s immune system when administered.Vaccines stimulate the body to make antibodies—proteins that specifically recognize and target the disease-causing bacteria and viruses, and help eliminate them from the body before they cause disease.Vaccines are frequently given by injection (a shot), but some are given orally and one is given via nasal spray.

There are several types of vaccines:live-attenuated, inactivated (whole or subunit), and toxoids.Live-attenuated vaccines contain a living bacteria or virus that has been weakened in the laboratory so that it doesn’t cause the actual disease in individuals with healthy immune systems.However, because they contain a small amount of the weakened live virus or bacteria, they should not be taken by people with incompetent or weakened immune systems.One example of a live attenuated vaccine is the Measles, Mumps and Rubella Virus Vaccine, Live.

Inactivated vaccines can be safely given to individuals with weakened immune systems.However, for such individuals, additional (booster)doses may be required to achieve immunity (protection).One example of a whole inactivated vaccine is the Poliovirus Vaccine Inactivated.

Scientists discovered that in some cases, the entire virus or bacteria is not required to elicit protective immunity and prevent disease; just a portion or a “subunit” of the disease-causing bacteria or virus is needed to provide protection.One example of a subunit inactivated vaccine is the Hepatitis B Vaccine, Recombinant.

Some bacteria cause illness by secreting a poison or toxin.Scientists discovered that inactivating the toxins, to create toxoids, and administering the toxoid can also protect individuals against the disease.One example of a toxoid vaccine is the Diphtheria toxoid vaccine.

Vaccines are available as single valent (one strain), multi-valent (several strains such as the seasonal influenza vaccine which has three strains of influenza virus)or combination vaccines (more than one virus or bacteria, such as MMR which contains measles, mumps and rubella viruses).