The Truth About Vaccine Shedding

What is vaccine shedding?

Vaccine shedding is when an individual releases, or sheds, the components of a vaccine either inside or outside of their body.

This can only happen with a certain type of vaccine called a live-attenuated vaccine. Some examples of live-attenuated vaccines that are commonly given in the United States include the:

measles, mumps, and rubella (MMR) vaccine
flu nasal spray vaccine (FluMist)
chickenpox vaccine
rotavirus vaccine

Live-attenuated vaccines contain a weakened form of a pathogen. These types of vaccines need to replicate within the body in order to produce an immune response.

Due to their weakened nature, the pathogens in these vaccines don’t cause disease. The exception to this is in immunocompromised individuals, for which live-attenuated vaccinations aren’t typically recommended.

Because live-attenuated vaccines can replicate, the weakened pathogen can be shed. But it’s important to note that shedding doesn’t equate with transmission, in which the weakened pathogen is passed to another person.

Should these pathogens be passed to another individual, they’re highly unlikely to cause disease. In fact, the only live-attenuated vaccine associated with significant infections due to shedding is the oral polio vaccine, which is no longer in use in the United States.

Which vaccines do shed?

It’s technically possible for any live-attenuated vaccine to shed. But in most instances, documented cases of this are rare.

The oral polio vaccine (OPV) is responsible for the most harmful infections related to vaccine shedding. The live-attenuated virus used in this vaccine can be shed from the body in feces.

In very rare cases, the virus used in the OPV can mutate and become harmful, potentially leading to paralysis. In countries that still use the OPV, this is estimatedTrusted Source to occur in 2 to 4 out of every million live births each year.

Since the year 2000, the OPV is no longer licensed or available in the United States. Now, all polio vaccines given in the United States are inactivated vaccines.

Do any of the COVID-19 vaccines shed?

The only COVID-19 vaccines that are currently authorized for emergency use are mRNA vaccines and viral vector vaccines. While you may have seen posts on social media about COVID-19 vaccines shedding, this is a myth. COVID-19 vaccines cannot be shed.

This is because none of the COVID-19 vaccines contain live SARS-CoV-2, the virus that causes COVID-19. The only COVID-19 vaccines that are currently authorized for emergency use are mRNA vaccines and viral vector vaccines.

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