A vaccine is a biological preparation that offers active acquired immunity to a specific disease. Generally, a vaccine comprises of an agent that has a resemblance to the disease-causing microbe. It is mostly made from a dead or weakened form of the microorganism or its toxins, or one of its surface proteins. When the vaccine is injected to a person’s body, it triggers or stimulates the immune system of the receiver’s body to recognise the agent as a foreign body or threat and annihilate it, while also storing information about it. In this way, whenever a future encounter happens with the microbe, the vaccinated body is immune to the infection. The different types of vaccines are inactivated vaccine, attenuated vaccine, toxoid vaccine, subunit vaccine, conjugate vaccine, valence vaccine, heterotypic vaccine and many experimental vaccines also.