Vaccine shedding

Vaccine-induced viral shedding (erroneously termed vaccine shedding) is a form of viral shedding^[1] following a viral infection caused by a statistically insignificant number^{[citation needed]} of administrations of attenuated (or "live virus") vaccines, which is a specific vaccine technology that uses an attenuated form of a live virus. The overwhelming majority of vaccines, however, are not attenuated (live virus) vaccines,^{[citation needed]} and therefore cannot cause vaccine-induced viral shedding, and only a statistically insignificant number of viral infections from those types of vaccines have ever been recorded.^{[citation needed]}

The specific use of the term "vaccine shedding"—which erroneously suggests the vaccine is being shed rather than the virus received in one—has risen to public prominence through anti-vaccine activists linked to misinformation relating to COVID-19, even though none of the COVID-19 vaccines authorized in the United States use live-virus vaccine technology.^[2] Despite this, a COVID-19 "vaccine shedding" conspiracy theory has consequently emerged, leading to vaccine hesitancy among some people.^[3][4][5]

Among the claims is that those inoculated with COVID-19 vaccines (which have largely used mRNA or viral vectors) may shed coronavirus spike proteins that can affect the fertility and menstruation of women who are exposed to them.^{[6][3][7][8][4]} With the exception of the oral polio vaccine (OPV), which was discontinued in the USA in 2000,^[9] 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.^[10]

Shedding is only possible, but even so, unlikely, with an attenuated vaccine, and it is impossible with other vaccine technologies such as inactivated vaccine (killed-virus vaccines), viral vector vaccine, RNA vaccines,^[5] 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. Nevertheless, not all pathogens are shed;shedding does not equal transmission^{[clarification needed]}; and transmission does not always cause disease.^{[citation needed]}

Occurrences[]

The only human vaccine to have caused any significant number of infections is the oral polio vaccine (OPV),^[9][11] and this vaccine is no longer used in developed countries.^[9] However, the OPV is still used in Asia and Africa, leading to a small number of vaccine-induced polio infections each year.^[12]

In 2016, the formulation of the OPV was changed to remove the already extinct and most problematic type 2 polio strain from the OPV.^[12] The route of infection is through contact with faeces, and some live vaccines, like the viruses they prevent, are shed in stool for up to 28 days.^[13] Normal hygiene is sufficient to prevent infection among healthy individuals,^[14] but immunocompromised individuals need to be especially diligent.^[15]

Other attenuated vaccines show no significant viral shedding, and inadvertent infection is rare.^[16] For example, only eleven cases of chickenpox transmission by vaccinated individuals have been documented out of approximately fifty million doses,^[17] and but a single documented case of influenza virus transmission, and that person remained asymptomatic.^[18]

The attenuated virus from vaccines is much weaker and less likely to infect than the wild virus.^[19]

In dogs, vaccine-induced viral shedding has been observed with live attenuated Canine parvovirus vaccines.^[20]

Research[]

Regulatory authorities in the USA and EU recommend that shedding data should be collected both during the development phase of a new product and during clinical trials. A full report on shedding must subsequently be included in the Biologics license application.^[21][22]

A study of 345 participants aged 5–49 years who received the live influenza virus vaccine LAIV3, and for whom shedding was assessed by viral culture of nasal swabs (daily for days 1–7 post vaccination, every other day for days 9 through 25, and on day 28) indicated that 30 percent had detectable virus in nasal secretions obtained by nasal swabbing. In an open-label study of 200 children aged 6–59 months who received a single dose of LAIV3, shedding of low titers of at least one vaccine virus was detected on culture in 79 percent of children and was more common among the younger recipients. Serious illnesses have not been reported among unvaccinated persons infected inadvertently with vaccine viruses. The estimated probability of transmission of vaccine virus within a contact group with a single LAIV recipient in this population was 0.58 percent.^[23]

References[]