VACCINE AND ITS TYPES

Vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins. The agent stimulates the body's immune system to recognize the agent as foreign, destroy it, and "remember" it, so that the immune system can more easily recognize and destroy any of these microorganisms if it encounters in future.

Types of vaccines:

a) Inactivated vaccines: When inactivated vaccines are made, the bacteria are completely killed using a chemical, usually formaldehyde. Dead pieces of disease-causing microorganisms (usually bacteria) are put into the vaccine. Because the antigens are dead, the strength of these vaccines tends to wear off over time, resulting in less long-lasting immunity. So, multiple doses of inactivated vaccines are usually necessary to provide the best protection. The benefit of inactivated vaccines is that there is zero chance of developing any disease-related symptoms -- allergic reactions are possible but extremely rare.

Examples of inactivated vaccines are hepatitis A, hepatitis B, poliovirus, hemophilic influenza type b, meningococcal, pneumococcal and the injected form of influenza.

b) Live-attenuated vaccines: Live-attenuated basically means alive, but very weak. These vaccines are made when the virus is weakened to such a level that they reproduce only about 20 times in the body. 

When the vaccine is made, the virus or bacteria is weakened in a laboratory to the point where it's alive and able to reproduce, but can't cause serious illness. Its presence is enough to cause the immune system to produce antibodies to fight off the particular disease in the future. They typically provoke more durable immunological responses and are preferred for healthy adults.

Examples include the viral diseases yellow fever, measles, rubella, and mumps and the bacterial disease typhoid. 

c) Recombinant Vector vaccine – by combining the physiology of one micro-organism and the DNA of the other, immunity can be created against diseases that have complex infection processes.

d) DNA vaccination – in recent years a new type of vaccine called DNA vaccination has been created from an infectious agent's DNA. As in complex diseases the DNA quality of the infection changes thus no vaccine works on it.DNA vaccine works by insertion and expression, triggering immune system recognition of viral or bacterial DNA into human or animal cells. Some cells of the immune system that recognize the proteins expressed will mount an attack against these proteins and cells expressing them.