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