Although now at the forefront of molecular technologies, vaccination has a history in the West going back at least 200 years (vacca - 'cow' refers to Edward Jenner's use of cowpox against smallpox).  The basic idea is unchanged: to introduce one or more foreign antigens in the hope of stimulating a protective immune response to destroy or disable the pathogen.  Often this approach seeks to mimic the natural immunity to infection which develops to diseases of poverty, sometimes after only a single episode.

Whatever the mechanism, a vaccine has three components:

  1. Antigen(s) - parts of the pathogen introduced to stimulate a specific, protective immune response

  2. Adjuvant - given to boost the immune response, for example by presenting the antigen in a certain way

  3. Platform - mechanism (e.g. viral vector) by which the vaccine is introduced and (if applicable) is replicated within the host

Modern vaccines are of several broad types according to how the antigen is introduced.

  • Attenuated vaccines contain either a live but weakened (non-pathogenic) form of the whole pathogen, or a pathogen which has been killed.

  • Subunit vaccines and virus-like particles contain proteins from the pathogen, produced either by purification or - more commonly today - in an engineered bacterium such as E. coli.

  • Recombinant Deoxyribonucleic Acid (DNA) vaccines contain some or all of the gene(s) for expression of the antigen(s) within a suitable molecule.

Although some of the most successful vaccines have been live attenuated forms (e.g. measles vaccine, oral polio vaccine), most modern vaccines are based on recombinant DNA technologies in some shape or form.  They often seek to express several key antigens simultaneously within the host.