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| 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
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