[Mercola]: When you're infected with a virus that causes an illness, that virus is shed in your saliva and other bodily fluids, and sometimes also via skin lesions. This means that a person who comes into direct contact with the shed virus may also become infected. The same holds true for live attenuated viral vaccines.
While inactivated vaccines use a killed version of the pathogen, live viral vaccines use a weakened (or attenuated) version of the virus. Typically, the live virus used in vaccine production is passed through a living cell culture or other host, such as chicken embryo, many times over until it becomes weakened to a point that it's not likely to make you sick when it's injected or, in the case of live oral vaccines, swallowed.
That being said, a live vaccine strain virus is still active and strong enough to trigger an inflammatory response in your body, prompting the creation of vaccine-acquired antibodies. There are a few problems with this, such as the possibility that the weakened vaccine-strain virus can revert to virulence, leading to serious complications identical or similar to complications of the natural disease the vaccine is supposed to prevent in the vaccinated person.1
Another noted problem is that the person who is given a live attenuated viral vaccine can asymptomatically shed and transmit vaccine-strain virus for a period of days, weeks or months and potentially infect close contacts, who can also experience symptoms of the very disease the vaccine was intended to prevent...read more>>>...