Categories of Vaccinations
Immunizations teach your body how to defend itself when germs such as viruses or bacteria invade. The first human vaccines against viruses were based using weaker viruses to generate immunity. The smallpox vaccine used cowpox, a poxvirus that was similar enough to smallpox to protect against it but usually didn't serious illness. Rabies was the first virus attenuated in a lab to create a vaccine for humans.
Vaccines are made using several different processes. They may contain live viruses that have been weakened or altered so as not to cause illness; inactivated or killed organisms or viruses; inactivated toxins; or merely segments of the pathogen.
Live vaccines are prepared from live organisms. These organisms are passed through chick embryos until they lose their ability to induce the disease fully, but retain the ability to trigger off the defense mechanism. Live vaccines are usually stronger than inactivated vaccines. They multiply within the host and produce more antigens. The vaccine used to immunize a patient against a disease falls into one of four categories:
- Attenuated live viruses. These are weakened viruses.
- Killed viruses or bacteria. These are dead viruses.
- Toxoid. These contain a toxin produced by a bacterium.
- Biosynthetic. These contain synthetic substances.
Certain organisms when killed by heat or chemicals and then introduced into the body induce immunity. Killed vaccines are not as effective as live vaccines. These are administered by injections. Some vaccines are prepared from fractions of the cell. These vaccines are safe and effective but for a limited duration. Diphtheria, Pertussis and Tetanus vaccine is given in a single shot.
Some vaccines combine two strains of the same species. Polio and influenza vaccines are prepared this way. Some vaccines are made from toxins. In these cases, the toxin is often treated with aluminium or adsorbed onto aluminium salts to decrease the toxin's harmful effects. After the treatment, the toxin is called a toxoid. Vaccines made from toxoids often induce low-level immune responses and are therefore sometimes administered with an adjuvant, an agent that increases the immune response.
