Vaccines - Pharmacology

The immune system develops antibodies to attack a pathogen using one of two methods: active immunity and passive immunity.

Active immunity occurs when the immune system generates antibodies on the first exposure to the pathogen. This immune response is relatively slow, resulting in the patient showing the signs and symptoms of the disease.

However, the immune system remembers the pathogen and is quick to dispatch antibodies should the pathogen attack a subsequent time. This happens faster than the initial response and can generally eliminate the pathogen before the patient experiences the signs and symptoms of the disease. The patient may have a life long immunity to the pathogen thanks to the body’s active natural immunity.

Active natural immunity can also occur through immunization when the patient receives a vaccination against the pathogen. The vaccination contains a small amount of the pathogen to stimulate the production of antibodies, but insufficient in strength to develop the signs and symptoms of the disease.

There are five ways in which the pathogen in vaccines is produced.

  1. Whole or components of an inactivated (dead) microorganism
  2. Live, but weakened microorganisms
  3. Toxoids, which are inactivated toxins produced by some microorganisms
  4. Conjugates, which are vaccines that link a protein (toxoid) from an unrelated organism to the outer coat of the disease-causing microorganism. The result is a substance that is recognized by the immature immune system of young infants. Haemophilusinfluenzaetype b is an example.
  5. Recombinant subunit vaccine is where DNA of a pathogen is inserted into a cell or organism. The cell or organism then produces massive quantities of the pathogen that are used in place of the whole pathogen. Examples are hepatitis B and LYMErix for Lyme disease.

A booster dose of a vaccine is sometimes required to maintain sufficient immunity. The immune system has a memory and when the vaccinated individual is later exposed to the actual pathogen, the body can mount a rapid immune response and prevent the disease. This is called artificially acquired immunity.

Passive immunity occurs when the patient receives antibodies from another source rather than generating his or her own antibodies. Newborns have natural passive immunity to protect them from pathogens. The newborn receives natural passive immunity from antibodies that cross the placenta. Antibodies mayalso be acquired from a pool of antibodies from human or animal sources. This is acquired passive immunity.

Passive immunity is transient lasting no more than several weeks to a few months. The individual does not mount his or her own immune response to antigens. Acquired passive immunity is important when time does not permit active vaccination alone, when the exposed individual is at high risk for complications of the disease, or when the person suffers from an immune system deficiency that renders that person unable to produce an effective immune response.

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