- Vaccine is an artificial biological preparation that contains antigens or mixture of antigens to acquired active immunity to the particular infectious disease.
- Vaccine is prepared by the various different substances like disease causing microorganism or weakened or killed form of microbe, can be from one of the surface protein or its toxins.
- Agent used in vaccine stimulates body’s immune system which recognise the antigen and destroy it and also encounter the agent if in future that antigen enters in the body.
- Vaccine is prophylactic (prevent future infection by the pathogens) or therapeutic (fight against the disease already occurred).
- The process of administration of vaccine is called vaccination; it is the most effective method to prevent infectious diseases.
- The term vaccine and vaccination are coined by Edward Jenner. He described that how cowpox is to produce immunity against smallpox.
- Vaccine stimulates T-cells and B- cells which further produces antibodies against the antigen.
- The first vaccine was introduced by Edward Jenner, used the cowpox virus to protect against smallpox in humans
- Prior to this Asian physician used to give dried lesions from the diseased person to children. But by this process some individuals developed immunity while some develop disease.
- Jenner introduced a safer way to counter this disease. He uses similar cowpox virus to confer immunity against smallpox (rare condition in which immunity of one virus protect against another virus).
- Louis Pasteur in 1881 shows immunization against anthrax disease and four years later he develops vaccine of rabies.
Characteristics of vaccine:
- Long term protection
- Induced b and t cells
- No or very few side effect
- Low cost and biologically stable
- Easy to use
Types of vaccine:
- Is containing live organism which is weakened in the lab so that it cannot cause disease and activate the immune system against the antigen.
- It is relatively easy to produce live attenuated vaccine for viruses then bacteria because bacteria have thousands of genes which is much harder to control.
- Uses whole organism as vaccine which loses their pathogenicity but can induce immune response, they continuously multiply in human and provide immunity over the period of time.
- Examples of live attenuated vaccine are mumps vaccine, measles vaccine, chickenpox, BCG, Sabin’s polio vaccine.
Killed or inactivated vaccine:
- Microorganism causing diseases are killed by the means of chemicals, heat or radiation. These are more stable and safer than live vaccines reason is that the dead microorganism cannot mutate back to cause diseases.
- They are the easiest preparations to use
- Chemical which are used to kill microorganism are formaldehyde or beta-propiolactone, traditionally used chemical for virus is formalin.
- The process should be observed carefully because excessive treatment can destroy immunogenicity and insufficient treatment leave infectious microbes to cause disease.
- Example: anthrax vaccine, cholera vaccine, purtusis vaccine, hepatitis vaccine, salk polio vaccine.
- Like above it doesn’t uses whole organism, only the part which server as antigen and stimulate the immune system is used to prepare vaccine.
- Composed of purified macromolecule derived form the pathogen known as subunit vaccine.
- General forms of such vaccine are
Purified capsular polysaccharide vaccine: pathogenicity of some bacteria depend on their capsule and this capsule protect bacteria from binding to the antibody. In this way infants and younger children’s immune system cannot recognise and respond against them.Example: Hib vaccine, vaccine for Streptococcus pneumoniae
Recombinant microbial vaccine: various genes encoding surface antigen of viral, bacterial and protozoan pathogens were successfully cloned into the cells of a vector. This genetic material is in bacteria cause to represent other microbial gene on its surface i.e. harmless bacterium mimics the harmful microbe and provide immunity against it. Hepatitis B is the only recombinant vaccine at present.
Synthetic peptide: development of synthetic peptide vaccine depends on the immunogenic sites. They have many advantages like low cost production and relatively stable.it is not applicable for all viruses like polio virus.
Inactivated exotoxin: this vaccine is made for some bacteria that produce toxins or harmful chemical substances. This toxins or inactivated(toxoid) by formalin and serve as vaccine which produces the anti-toxoid antibodies and neutralizes the toxin. Example of such vaccine is diphtheria and tetanus vaccine.
- The DNA vaccine is the DNA sequence used as vaccine.
- The sequence is responsible for the antigenic activity of the pathogen.
- The gene of the microbe’s antigen is introduced in the body the host cell take up the DNA, DNA instruct to produce the antigen molecule which is represented by the cell on its surface, now the body’s own cells become the vaccine producing factory and stimulates the immune system.
- Immune response is raised against the protein produces by the cell
- Example: DNA vaccine against west nile virus, herpes and influenza virus.