Virus shedding refers to the process when a person is infected by a virus that transmits it onto others, causing infection. Simply said, it is one of the ways COVID-19 predominantly spreads when an infected and contagious person transmits whole viral particles, or parts of the virus onto others.
With respect to vaccines, since some types of vaccines are made using a form of live virus, or contains fragments of the virus, it is believed that a person who has just been vaccinated, or administered the vaccine dose recently is at high risk of spreading the virus onto others. The concerns have been raised in several parts of the world, with many establishments closing doors or imposing restrictions on vaccinated people.
Again, while most of the vaccine shedding beliefs have emerged from hesitant vaccine-takers, some have also believed on prior vaccine history to believe the myth. Some vaccines, such as the flu, typhoid vaccine actually contain bits of the weakened live virus (or are live-attenuated virus vaccines), which may cause a low level of shedding or pose a risk. However, even with those vaccines, the risk is rare or negligible.