Vaccine shedding is a form of viral shedding[1][2] which can occasionally occur following a viral infection caused by an attenuated (or "live virus") vaccine. Illness in others resulting from transmission through this type of viral shedding is rare.[3][4] Most vaccines are not attenuated (live virus) vaccines,[5] and therefore cannot cause vaccine-induced viral shedding, though the idea of shedding is a popular anti-vaccination myth.[6]
The specific use of the term "vaccine shedding" has risen to public prominence through anti-vaccine activists linked to misinformation related to COVID-19, who erroneously claim that COVID-19 vaccination can cause individuals to shed coronavirus spike protein and affect menstruation and fertility in women exposed to them.[7][3][8][9][10] However, the spike protein generated by vaccination does not shed, and there is no evidence to suggest that these vaccines cause menstruation and fertility problems.[3][11] Vaccination also cannot cause shedding of the COVID-19 virus since none of the COVID-19 vaccines authorized for use by the FDA or the World Health Organization as of December 2021 are live-virus vaccines.[12][13] Despite this, a COVID-19 "vaccine shedding" conspiracy theory has subsequently emerged, leading to vaccine hesitancy among some people.[3][10][14]
Shedding is only possible with an attenuated vaccine. It is impossible with other vaccine technologies such as inactivated vaccine (killed-virus vaccines), viral vector vaccine, RNA vaccines (that contain no virus),[14] or subunit vaccines (a vaccine technology using only isolated proteins of a virus). Only a small number of vaccines use technology that contain live virus which can theoretically infect others.
With the exception of the oral polio vaccine (OPV), there have been no documented cases of vaccine-induced viral shedding that has infected contacts of a person vaccinated with an attenuated (live-virus) vaccine.[15]