A vaccine is a manufactured drug that helps the body fight certain diseases, a vaccine is usually made using a weak version of the virus or disease that is introduced into the body so that your white blood cells can be trained for when the real threat arrives. The website www.wikipedia.com defines a virus as "A biological preparation that enhances immunity to a particular disease. A vaccine typically contains an agent that resembles a pathogenic microorganism and is often made up of weakened or killed forms of the microbe, its toxins or one of its surface proteins." The first ever vaccine was created around 1796 by a man named Edward Jenner who created a smallpox vaccine using cowpox. He did this by observing that those who had had cowpox could not contract smallpox. He first tested it on an eight year old boy where he infected him with cowpox and once he recovered he infected him with smallpox and the child showed no symptoms. This procedure was not that risky because the effects of cowpox were not fatal but smallpox was. Nowadays, vaccines have evolved mainly due to the introduction of microscopes and biological engineering in the fields of medicine. There are three types of vaccines used today: live or attenuated vaccine, killed vaccines, and toxoid vaccine. Live or attenuated vaccine is a vaccine produced by weakening or even removing harmful parts of a pathogen or virus. This type of vaccine is used as a kind of practice to help the body's immune system develop a way to fight off the inert pathogen before an active one invades the body. These vaccines are produced by passing through foreign hosts, e.g. tissue culture, embryonated eggs. and Live animals. Examples of these vaccines are the measles vaccine...... middle of paper ......cal, -. -., -. "What are vaccines?" What are vaccines? Medical news, -. Network. 09 February 2014. .* Who, -. -., -. "Vaccines." WHO. WHO, -. Network. 08 February 2014. .* Wikipedia, -. -., -. “Weakened vaccine.” Wikipedia. Wikimedia Foundation, 14 January 2014. Web. 08 February 2014. .* Wikipedia, -. -., -. "Inactivated vaccine." Wikipedia. Wikimedia Foundation, 21 January 2014. Web. 09 February 2014. .* Wikipedia, -. -., -. "Toxoid." Wikipedia. Wikimedia Foundation, 13 January 2014. Web. 08 February 2014. .* Wikipedia, -. -., -. "Vaccine." Wikipedia. Wikimedia Foundation, 31 January 2014. Web. 06 February. 2014. .