Over the last century, vaccination has been the most effective medical strategy to control infectious diseases. Smallpox has been eradicated world-wide and poliomyelitis has been almost eradicated. Most viral and bacterial diseases traditionally affecting children world-wide are now preventable by vaccines. Vaccination is estimated to save at least 2-3 million lives every year.
What is vaccine?
Vaccine is an immune-biological substance designed to
produce specific protection against a given disease.
It stimulates the production of protective antibody and
other immune mechanisms.
Vaccines may be prepared from live modified organisms,
inactivated or killed organisms, extracted cellular functions, toxoids or
combination of these.
Types of Vaccine
- Live vaccines
- Inactivated or killed vaccines
- Subunit vaccines
- Combinations
A. Live Vaccines
- Live vaccines are prepared from live or wild organisms.
- These organisms have been passed repeatedly in the laboratory in tissue culture or chick embryos and have lost their capacity to induce full-blown disease but retain their immunogenicity.
- Live vaccines are more potent immunizing agents than killed vaccines, the reasons being: (a) Live organisms multiply in the host and the resulting antigenic dose is larger than what is injected. (b) Live vaccines have all the major and minor antigenic components. (c) Live vaccines engage certain tissues of the body, as for example, intestinal mucosa by the oral polio vaccine. (d) There may be other mechanisms such as the persistence of latent virus.
- When two live vaccines are required, they should be given either simultaneously at different sites.
- In the case of vaccines, protection is generally achieved with a single dose of vaccine. An additional dose is given to ensure seroconversion.
- The second dose is given to ensure that 100% of persons are immune.
- Polio vaccine which needs three or more doses to be given at spaced intervals to produce effective immunity.
- BCG (Bacille Calmette-Guerine), Yellow Fever, OPV (Oral Polio Vaccine), Measles, Mumps, Rubella, Typhoid, Rotavirus, and Cholera vaccines are the example of live vaccines.
Contraindications of Live vaccines
- Person with immune deficiency disease.
- Persons immune response may be suppressed because of leukaemia, lymphoma or malignancy or because of therapy with corticosteroids, alkylating agents, antimetabolic agents or radiation.
- Pregnancy is another contraindication.
B. Inactivated or killed vaccines
- Inactivated vaccines are produced by growing virus or bacteria in culture media and then inactivating them with heat and chemicals (usually formalin), when injected into the body they stimulate active immunity.
- Inactivated or killed vaccines are usually safe but generally less efficacious than live vaccines.
- Killed vaccines usually require a primary series of 2 or 3 doses of vaccine to produce an adequate antibody response, and in most cases ‘booster’ injections are required.
- Inactivated vaccine is also given to immunodeficient person.
- The only absolute contraindication to their administration is a severe local or general reaction to a previous dose.
- Example of killed vaccine: Typhoid (killed), Cholera (killed), Plague, Pertussis, Influenza, Typhus, Polio (IPV), Rabies, Japanese encephalitis (JE), Tick-borne encephalitis (TBE), and Hepatitis A virus (HAV).
C. Subunit vaccines
A vaccine can be made of single or multiple antigenic components of a microorganism that are capable of stimulating a specific immune response sufficient to protect from the relevant pathogen infection or from the clinical manifestation of disease.
There are five types of Subunit vaccines are:
- Toxoids
- Protein vaccines
- Recombinant protein vaccines
- Polysaccharide-based vaccines
- Conjugated vaccines
1. Toxoids
- The toxins produced by the organisms are detoxicated and used in the preparation of vaccines.
- The antibodies produced neutralize the toxic moiety produced during infection, rather than act upon the organisms
- In general, toxoid preparations are highly efficacious and safe immunizing agents.
- Diphtheria and Tetanus toxoids vaccines are examples of toxoids.
2. Protein vaccines
- A single protein or a combination of proteins from a pathogen is sufficient to stimulate a protective immune response.
- Proteins can be purified from in-vitro cultures of a pathogenic microorganism.
- Licensed acellular pertussis vaccines currently available contain from two to four different proteins purified from B. pertussis.
- Most widely used subunit protein vaccines is the influenza vaccine composed of haemagglutinin and neuraminidase purified from the inactivated influenza virus.
3. Recombinant protein vaccines
- Vaccines are developed by the recombinant deoxyribonucleic acid (DNA) technology.
- Recombinant proteins are generally better purified from cultured microorganisms resulting in cleaner vaccine preparations with a better safety profile.
- Hepatitis B vaccine, Lyme disease, and Cholera toxin B are example of these vaccines.
4. Polysaccharide-based vaccines
- Polysaccharide-based vaccines are produced by presence of polysaccharide coat on the bacteria outer membrane.
- Antibodies to bacterial surface polysaccharides can clear the bacteria from the host by different mechanisms, such as complement-mediated killing and opsonophagocytosis.
- A limitation of polysaccharide-based vaccine is that the immune responses they elicit are often serotype specific.
- Pneumococcus, Meningococcus, Hib, and Typhoid (Vi) vaccine are example of polysaccharide-based vaccine.
5. Conjugated vaccines
- Children under two years of age do not respond well to antigens, such as polysaccharides, which produce antibodies via a T-cell independent mechanism.
- If these polysaccharide antigens are chemically linked (conjugated) to a protein that T-cells recognize, then these conjugate vaccines can elicit strong immune responses and immune memory in young children.
- Similar to polysaccharide-based vaccines, the conjugate vaccines are also sero-type specific, and therefor, multivalent formulations are required to achieve protection against multiple serotypes.
- S. pneumococcal and meningococcal vaccines are the example of conjugated vaccines.
D. Combinations of vaccines
If more than one kind of immunizing agent is included in the
vaccine, it is called a mixed vaccine.
The aim of combined vaccines is:
- Simplify administration.
- Reduced costs.
- Minimizing the number of contacts of the child with the health system.
- Reducing the storage cost.
- Improving timelines of vaccination and facilitating the addition of new vaccine into immunization programme.
The following are some of the well-known combination of
vaccines Eg. DPT; DT; DP; DPT and typhoid vaccine; MMR; DPT plus inactivated
polio vaccine; Hepatitis A and B; Hepatitis A and Typhoid; Pentavalent; or DTwP
(Deptheria, tetanus, whole-cell pertussis).
National Immunization Schedule of India
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| National Immunization Schedule of India |
*Abbreviation used in National Immunization schedule of India:
BCG-Bacille Calmette-Guerin; MR-Measles
& Rubella; DPT-Diphtheria, Pertussis, Tetanus; PCV-Pneumococcal
conjugate vaccine; fIPV-Fractional inactivated polio vaccine; IM-Intramuscular;
SC-Subcutaneous; ID-Intradermal;
Pentavalent-Diphtheria, Pertussis, Tetanus, Hepatitis B, Haemophilus influenza type
B.
Storage of vaccines in Ice Line Refrigerator (ILR)
.jpg "Storage of vaccines in Ice Line Refrigerator (ILR)") |
Storage of vaccines in Ice Line Refrigerator (ILR) |
Wastage rate of vaccines acceptable in India
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Maximum acceptable wastage vaccines |
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