Do Vaccinated People ‘Shed’ COVID-19 Vaccine Particles?

As the COVID-19 pandemic coursed its way through a second year, misinformation surrounding the origin of the novel coronavirus, its variants, and rumors surrounding vaccines persisted. One such claim was that individuals vaccinated against COVID-19 can shed viral components that are capable of infecting and harming those around them.

Snopes readers asked our team to investigate whether this was true. We found this claim to be false. It is true vaccines containing a weakened version of a virus, known as live attenuated vaccines, can sometimes cause shedding. However, none of the COVID-19 vaccines authorized for use in the U.S. contain a live virus.

More on that below.

Tracing the Source of the Claim

Since at least spring 2021, claims spread that vaccinated people can “shed” elements contained within the COVID-19 vaccines that may harm unvaccinated individuals. A closer look at the various iterations of the claim revealed that the controversial and conspiracy-touting medical group, America’s Frontline Doctors, issued a “press release” in April that made unproven claims about COVID-19 vaccine shedding, PolitiFact reported at the time. 

Such allegations resurfaced in the fall when a viral Oct. 27 blog post claimed that “Pfizer Confirms COVID-Vaccinated People Can ‘Shed’ Spike Proteins And Harm The Unvaccinated,” noted Poynter.

COVID-19 Vaccines Currently Available in US

Viral shedding occurs when an infected person sheds virus particles from their nose and mouth, which is an entirely real phenomenon and the reason masks have been effective in preventing the spread of COVID-19. Vaccine shedding, on the other hand, refers to the release of vaccine components outside of the body. While it is true that some vaccines containing a weakened version of a virus can cause shedding, none of the vaccines authorized for use in the U.S. contain one.

As of this writing, two types of vaccines are currently available under emergency use authorization in the U.S.: mRNA vaccines like Comirnaty (formerly Pfizer-BioNTech) and Moderna. The mRNA vaccines do not contain a live virus but instead teach the body to make a piece of a “spike protein” that is found on SARS-CoV-2 and causes COVID-19 infection.

“After making the protein piece, cells display it on their surface. Our immune system then recognizes that it does not belong there and responds to get rid of it,” wrote the Centers for Disease Control and Prevention (CDC). “When an immune response begins, antibodies are produced, creating the same response that happens in a natural infection.”

By comparison, the one-shot Johnson & Johnson is a more traditional, viral vector vaccine that contains a modified piece of a common virus known as an adenovirus — which is not necessarily a coronavirus — that exposes the body’s immune system without the ability to reproduce. 

Neither of the above contain SARS-CoV-2, the virus that causes COVID-19, and there is no evidence to suggest that the spike protein sheds. 

Vaccines that can shed are those known as live attenuated vaccines, which include those that protect against mumps and rubella. These vaccines release a small portion of the virus in the body to stimulate a live response. In some cases, this exposure can trigger disease in a recently vaccinated person. 

Understanding the So-called  ‘Pfizer Documents’ 

Some people who pushed back against vaccines referred to authentic documents published by Pfizer that were said to report the mRNA vaccine produced by the biopharmaceutical company can environmentally expose unvaccinated people to spike proteins contained within the vaccine, via inhalation or skin contact. (A phenomenon dramatically dubbed “humanicide.”) 

These documents do indeed describe clinical trial protocol for phases 1, 2 and 3, but as the research and healthcare center Nebraska Medicine reported in April 2021, such claims that vaccines can “shed” the virus are misrepresentations of actual data published by Pfizer. (We have linked to an archive of those documents here.) Some social media users republished the authentic title page of the clinical trial protocol but misrepresented its contents: 

Authentic title page of the Pfizer mRNA vaccine clinical trial protocol highlighted by social media. Image sent by Snopes readers

Before a clinical trial may begin, the U.S. Food and Drug Administration (FDA) requires researchers to submit a clinical trial protocol to describe the elements of the study, its goals, and how data is to be collected and reported. 

“On page 67 of this document, there’s a section titled ‘Regulatory Reporting Requirements for SAEs.’ SAEs stands for serious adverse events. In this section, the document lists events that should be reported, including various types of exposure. ‘Exposure’ just means that someone somehow came in contact with the substance being studied. And ‘study intervention’ refers to the vaccine itself — the medicine (intervention) being studied,” noted Nebraska Medicine. 

“This document is not discussing viral shedding, or even indicating that there’s a potential for viral shedding. It also is not actually reporting adverse events. It is just telling health care providers how to document and track various types of potential adverse events.” 

No Evidence to Suggest COVID Vaccines ‘Shed’ 

In summary, it is true that viral shedding can occur when an infected individual spreads viral particles via the nose and mouth, transmitting the virus to uninfected people. It is also true live attenuated vaccines can case vaccine shedding. However, there is no evidence to suggest that either of the two forms of COVID-19 vaccines, mRNA and viral vector vaccines, can cause viral or vaccine shedding that would result in infecting unvaccinated individuals. 

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