Vaccines: Introduction and Types

Vaccines: Introduction and Types


Vaccines: Introduction and Types

Vaccines are those immunological products that stimulate recipient's immune system to produce antibodies promoting the destruction of microorganisms and to neutralize toxins produced by bacteria.

The immunity provided by vaccines last for years. Two or several booster doses of vaccines are needed to provide immunity at intervals of days or weeks. This later booster doses are for secondary immune response sensitized by a previous dose.

Vaccines are mainly the immunogens produced by pathogens, these immunogens have the immuno system inducing properties but not the pathogenic properties.
The components of the microbes in a vaccine provide immunity to a specific disease caused by the specific microorganism.


There are five types of vaccines :
1. Live vaccine
2. Killed vaccine
3. Toxoid vaccine
4. Bacterial cell component vaccine
5. Viral subunit vaccine.


1. Live vaccine:

Live vaccines are prepared from live bacteria or viruses causing infection without symptoms after the vaccines are given.
Attenuated vaccines are the live vaccines that have attenuated virulence of the microbes and the reduced ability to cause the disease.
In 1976, the first live vaccine was against small pox, produced by Edward Jenner.
Another example of live vaccine is live typhoid vaccine Ty 21a, that was produced by crippling the action of nitrosoguanosine on the DNA of a typhoid bacillus.
Current example of live vaccine is live measles, rubella, mumps and yellow fever vaccines.
Live vaccines don’t need booster doses and sometimes they may be virulent. But their immunity develops rapidly and lasts for a long time.

2. Killed vaccine:

Killed vaccines are the suspensions of
bacteria or viruses killed by heating or disinfectants such as formaldehydes or phenolic compounds.
Sufficient microbes are present in each dose of a killed vaccine to stimulate immune system.

Examples of killed vaccines are whooping cough or pertussis vaccine, typhoid vaccine, cholera, rabies vaccine and Salk typed polio vaccine.
Killed vaccines are safe in pregnancy and they cannot be returned to virulence.

Disadvantages of killed vaccines are that immunity takes long time to be developed and the manufacturing cost is high.


3.Toxoid vaccine:

Toxoid vaccines are prepared from bacterial toxins containing only the immunogenicity but not the toxicity.
Formol toxoid vaccines are prepared using 38% formaldehyde to eliminate toxicity.

In diphtheria and tetanus diseases, the infections are caused by the bacterial toxins diphtheria toxin and tetanospasmin, respectively. Toxoid vaccines are very effective against these diseases.


4. Bacterial cell component vaccine:

Bacterial cell component vaccines are prepared from components of bacterial cells.
These vaccines are specific and effective because they induce immunity against that component specifically.

Examples:  Haemophilus influenzae type B vaccine and Neisseriae meningitidis type A and type C vaccine prepared  from the capsular polysaccharides and the 23-valent pneumococcal polysaccharide vaccine.


5. Viral-subunit vaccine:

Viral-subunit vaccine is produced by disruption of viruses and from their released products.
Three common viral-subunit vaccines are - Hepatitis B vaccine and two influenza vaccines from neuraminidase and hemagglutinin.
But before that influenza viruses are cultured in an embryonated eggs and then they are treated with a surface active agent and disrupted releasing two subunits.

Hepatitis B vaccine is prepared using genetically engineered yeast cells that express HBs antigens.


" Vaccines: Introduction and Types"
Written By
Sadia Akhtar
Student of Department of Microbiology
Jagannath University.
Email- sadiabd810@yahoo.com

Post a Comment

0 Comments