Many types of vaccinations involve injecting dead parts or wholes of germ cells into people or animals to provoke a small immune response. In theory and in practice, this form of vaccination proves very successful, and when people or animals come in contact with the live germ cells, their bodies are already immune to them. Another form of vaccination is the live vaccine. This is injecting living parts or all of germ cells into a person/animal body to create immunity too.
Most live vaccine types, and there are many, are also called live attenuated vaccinations. This process of attenuation is extremely important because it makes injecting people with live germs to get immunity possible. Ordinarily, exposure to live germ cells would just end up making people sick with the virus or bacteria. With attenuation, this risk sharply reduces for healthy populations.
Essentially, attenuation is a process by which the germ or infectious parts of the virus or bacterium are reduced. This could be done in several ways, including placing a virus in an egg, often chicken, that contains an embryo, or infecting animals with a virus because they can fight it and change it. In this process, the virus or bacterium changes so that it is highly unlikely, but not impossible, to infect someone who receives a vaccination with the new virus form, but the vaccination will still confer immunity to people who get. The live vaccine is still very much live virus, but has changed into a form both less viral and more beneficial.
There are a number of vaccinations that are offered in live vaccine form. Oral polio has made use of the live poliovirus for many decades. Recently there has been a switch to more people receiving inactivated or dead poliovirus, due to concerns about possible contraction of the disease. It was always a risk when the vaccine was developed, but risk tended to be much lower than potential risk associated with contracting polio from a wild polio source. Usually infection with a live attenuated virus is milder than infection via contact with wild virus.
Other live vaccine forms include the nasal spray that is used as an alternative to the flu shot. This is an attenuated virus too. Some additional examples include chicken pox or varicella shots, measles, mumps, rubella (MMR) and vaccines against some forms of tuberculosis.
While most people are able to handle live vaccine shots, some people are told not to use them. People who have impaired immune systems are generally not advised to get live attenuated vaccinations. These pose heightened risk for contraction of illness.
Live vaccines potentially carry the risk of causing infection among people in perfect health too. Those concerned about this issue should speak to doctors regarding statistical chances of infection by vaccine compared to statistical likelihood of becoming extremely ill by not possessing immunity. One other thing people should know before getting a live vaccine is if they are allergic to eggs. Attenuation processes frequently use eggs and people may have allergic reactions to injections with certain live vaccines if they have previous egg allergies.