Immunization, also called vaccination or inoculation, a method of stimulating resistance in the human body to specific diseases using microorganisms—bacteria or viruses—that have been modified or killed. These treated microorganisms do not cause the disease, but rather trigger the body’s immune system to build a defense mechanism that continuously guards against the disease. If a person immunized against a particular disease later comes into contact with the disease-causing agent, the immune system is immediately able to respond defensively. Vaccines are classified into mainly four categories namely, Whole-Organism vaccines, Purified Macromolecules Vaccines, Recombinant Vaccines and Future Vaccines.
Classification of VACCINES:
I. WHOLE-ORGANISM VACCINES
a. Live attenuated vaccines
b. Killed or inactivated vaccines
II. PURIFIED MACROMOLECULES
b. Capsular Polysaccharide vaccines
c. Polypeptide vaccines
III. RECOMBINANT VACCINES
a. Recombinant Protein vaccines
b. Recombinant vector vaccines
c. Subunit Vaccines
d. Polynucleotide vaccines (DNA vaccine)
IV FUTURE VACCINES
a. Multivalent subunit vaccine
b. Anti-idiotype vaccine
c. Plant vaccine
Examples of Vaccines:
Examples of live attenuated vaccines include:
· Measles vaccine (as found in the MMR vaccine)
· Mumps vaccine (MMR vaccine)
· Rubella (German measles) vaccine (MMR vaccine)
· Oral polio vaccine (OPV) (sabin vaccine)
· Varicella (chickenpox) vaccine
· BCG (Bacillus Calmette-Guerin ) vaccine for TB
Examples of inactivated (killed) vaccines:
· Inactivated polio vaccine (IPV), which is the shot form of the polio vaccine
· Inactivated influenza vaccine
· Salk polio vaccine
· Pertussis vaccine used in DPT vaccine
Examples of toxoid vaccines:
· Diphtheria toxoid vaccine (may be given alone or as one of the components in the DTP, DTaP, or dT vaccines)
· Tetanus toxoid vaccine (may be given alone or as part of DTP, DTaP, or dT)
Examples of component vaccines:
· Haemophilus influenzae type b (Hib) vaccine
· Hepatitis B (Hep B) vaccine
· Hepatitis A (Hep A) vaccine
· Pneumococcal conjugate vaccine
Types of Vaccines:
Scientists have developed two approaches to immunization: active immunization, which provides long-lasting immunity, and passive immunization, which gives temporary immunity. In active immunization, all or part of a disease-causing microorganism or a modified product of that microorganism is injected into the body to make the immune system respond defensively. Passive immunity is accomplished by injecting blood from an actively immunized human being or animal.
Passive immunization is performed without injecting any antigen. In this method, vaccines contain antibodies obtained from the blood of an actively immunized human being or animal. The antibodies last for two to three weeks, and during that time the person is protected against the disease. Although short-lived, passive immunization provides immediate protection, unlike active immunization, which can take weeks to develop. Consequently, passive immunization can be lifesaving when a person has been infected with a deadly organism.
Occasionally there are complications associated with passive immunization. Diseases such as botulism and rabies once posed a particular problem. Immunoglobulin (antibody-containing plasma) for these diseases was once derived from the blood serum of horses. Although this animal material was specially treated before administration to humans, serious allergic reactions were common. Today, human-derived immune globulin is more widely available and the risk of side effects is reduced.
Vaccines that provide active immunization are made in a variety of ways, depending on the type of disease and the organism that causes it. The active components of the vaccinations are antigens, substances found in the disease-causing organism that the immune system recognizes as foreign. In response to the antigen, the immune system develops either antibodies or white blood cells called T lymphocytes, which are special attacker cells. Immunization mimics real infection but presents little or no risk to the recipient. Some immunizing agents provide complete protection against a disease for life. Other agents provide partial protection, meaning that the immunized person can contract the disease, but in a less severe form. These vaccines are usually considered risky for people who have a damaged immune system, such as those infected with the virus that causes acquired immunodeficiency syndrome (AIDS) or those receiving chemotherapy for cancer or organ transplantation. Without a healthy defense system to fight infection, these people may develop the disease that the vaccine is trying to prevent. Some immunizing agents require repeated inoculations—or booster shots—at specific intervals.
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