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Types of vaccines
Elaph Madallah
We will discuss We will discuss in the following sections
, each vaccine type has its own drawbacks and benefits
and types of vaccines that work best for one class of pathogen may not work at all for another.
Types of vaccines Live, attenuated
Killed or inactivated
Toxoid
Subunit
Peptide
Recombinant DNA vector
Attenuated vaccine
Live virus particles with very low virulence are administered
They will reproduce, but very slowly.
Since they do reproduce and continue to present antigen beyond the initial vaccination, boosters are required less often
There is a small risk of reversion to virulence, this risk is smaller in vaccines with deletions.
Attenuated vaccines also cannot be used by immunocompromised individuals
It is given by mouth as drops
Examples: 1. Vaccinia (smallpox)
2. Measles, mumps, rubella (MMR combined vaccine)
3. Varicella (chickenpox)
4. Influenza (nasal spray)
5. Rotavirus
6. Zoster (shingles)
7. Yellow fever
Adventage
Live attenuated microbes induce longer and greater immunity as they multiply in the body
Excretion of microbe by the vaccinated individual transmits it to other nonimmune contacts so that they also get vaccinated
Disadventage An important problem that
the live microbe may change back to normal microbe causing disease; only polio virus has this problem
Maintenance of cold storage
Should not be given to immunocompromised and pregnant woman
Killed or inactivated
An inactivated vaccine consists of virus particles which are grown in culture and then killed using a method such as heat or formaldehyde.
The virus particles are destroyed and cannot replicate, but the virus proteins are intact enough to be recognized and remembered by the immune system and evoke a response.
When manufactured correctly, the vaccine is not infectious, but improper inactivation can result in intact and infectious particles.
Since the properly produced vaccine does not reproduce, booster shots are required periodically to reinforce the immune response.
Disadventage
Adventage
Immunity is shorter and weaker
No immunity of the contacts
Cannot revert back to normal
No cold chain
Toxoid vaccine
is inactivated exotoxins of bacteria whose toxicity is destroyed but antigenicity is retained
e.g diphtheria and tetanus toxoid
Disadveantage Adventage
Only effective if disease caused solely by bacterial exotoxin
Avoids use of whole organism
Adjuvants
A chemical substance that can be added to a vaccine in order to enhance the immune response to the vaccine.
Able to enhance humoral and cell-mediated immune responses
Act as carriers for antigenic material:
E.g.
Aluminium phosphate/hydroxide
Aluminium potassium sulphate
Saponins
Aviridine
Alum
Aluminum phosphate/hydroxide Alum is an inorganic salt that
binds to proteins and causes them to precipitate.
Whenever the alum/vaccine complex is injected into the body, it slowly dissolves, releasing the vaccine.
Alum is the only adjuvant approved for use in humans.
Subunit vaccines containing only the antigenic parts of the
pathogen.
These parts are necessary to elicit a protective immune response.
Because these vaccines use only specific pieces of the germ, they give a very strong immune response that’s targeted to key parts of the germ.
They can also be used on almost everyone who needs them, including people with weakened immune systems and long-term health problems.
The effectiveness of subunit vaccines in increased by giving them in adjuvants
Examples
DTAP vaccine (The pertussis component is an example of a subunit vaccine)
Typhoid
Hepatitis B
Plague immunization
Adventage Disadventage
can safely be given to immuno-suppressed people
less likely to induce side effects.
isolated proteins may have a different three dimensional 'structure than the protein in its normal context, and will induce antibodieș that may not recognize the infectious organism.
Isolated protein does not stimulate the immune system as well as a whole organism vaccine.
May require intact cold chain.. Too large to fit into some delivery vehicles
need booster shots
PEPTIDE VACCINE
Use discrete portion (domain) of a surface protein as vaccine.
These domains are 'epitopes' (antigenic determinants) and capable to elicit an immune response
• In some cases, small peptides are often degraded and therefore show poor or no immune response.
• When these peptides are fused with a inert carrier proteins, vaccine exhibits stronger immune response
Adventage Disadvantage
Avoids use of whole organism
Precise composition of single epitope known
Small enough to fit into most delivery vehicles
Very stable
Only small, linear, non-conformational epitopes
May possess epitopes recognized by only a small number of HLA molecules
May be perceived as hapten if not conjugated to carrier
Rapidly dissipated in tissues, thus requires highly effective
adjuvant or delivery vehicle for immunogenicity
May be costly or difficult
Recombinant DNA vector vaccine Production of vaccine antigens by genetic engineering
Recombinant vaccines are those in which genes for desired antigens of a microbe are inserted into a vector.
Adventage Disadvantage Antibody response is
longer Cytotoxic T-cell response
Low cost manufacture
Greater stability
Easier storage and transportation
Still in development
Example Cholera toxin A can be safely removed from cholera toxin.
Since the genes for the desired antigens must be located, cloned, and expressed efficiently in the new vector, the cost of production is high.
When engineered vaccinia virus is used to vaccinate, care must be taken to spare immunodeficient individuals