What is a vaccine?

There are many definitions of what a vaccine is, ranging from very specific to very broad.


1-Vaccine means any preparation that elicits a humoral immune response and/or cellular mediated response in humans provided that in each case such a preparation contains one or more molecules or ingredients that elicit a specific immune response to one or more such molecules or ingredients and/or to a pathogenic micro-organism, including, without limitation, live attenuated or modified microorganisms, whole killed microorganisms, proteins, polysaccharides, polysaccharide conjugates, peptides, recombinant proteins, glycolipids and fragments thereof.

2- Vaccine means any substance used to stimulate the production of antibodies or other adaptive immune system-derived effect in vivo to provide immunity against one or several diseases, which is prepared from the causative agent of a disease, its products, or a synthetic substitute, and designed to act as an antigen without inducing the disease.

3- A suspension of live (usually attenuated) or inactivated microorganisms (e.g. bacteria or viruses) or fractions thereof administered to induce immunity and prevent infectious diseases and their sequelae. Some vaccines contain highly defined antigens (e.g., the polysaccharide of Haemophilus influenzae type b or the surface antigen of hepatitis B); others have antigens that are complex or incompletely defined (e.g. Bordetella pertussis antigens or live attenuated viruses). Ref : cdc

4- Vaccine means one or more biological and/or chemical materials that is or are designed to elicit an immune response in humans

The latest definition is so broad that basically anything can be called a vaccine, since anything foreign to the human body could trigger an immune response.

With those definitions in mind lets take a moment to visit the different types of vaccines that are licensed for used around the world:

Different types of vaccines