What Is 'Vaccine Shedding'? Why It Can't Happen With the COVID-19 Vaccines

None of the COVID-19 vaccines approved in the US put you at risk for this extremely rare occurrence.

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Getting a COVID-19 vaccine is often seen as a ticket to freedom. It allows you to skip quarantine requirements when vacationing in certain destinations, eat in a crowded restaurant with less fear of getting sick, and safely hug your elderly relatives.

But things looked a lot different in April 2021, when one store in Canada banned vaccinated customers from entering. The reason? People who've received a COVID-19 shot could "shed" the virus to others and cause harm, according to the store's owner. Say what?

Let's get something straight: The COVID-19 vaccines have a list of potential side effects, but endangerment to those around you isn't among the risks. Despite the facts about these new shots, misconceptions that they cause "vaccine shedding" have circulated on social media, stoking fear and fueling vaccine hesitancy.

Here's what to know about vaccine shedding, and why it's not something you need to worry about with the COVID-19 shots.

What Is 'Vaccine Shedding'?

Like many myths, the belief that interacting with someone who got a vaccine might cause you harm stems from a kernel of truth. It's a concept called viral shedding (or sometimes "vaccine shedding"), a process of the body releasing viral particles from a vaccine and hypothetically creating a risk of infection to others.

"It is possible to have viral shedding after a vaccine, but what that requires is a weakened virus to be used as the basis for the vaccines. That's not the basis or science behind any of the vaccines we're currently using for COVID-19," Vincent Venditto, PhD, assistant professor of pharmaceutical sciences at the University of Kentucky College of Pharmacy, who has worked on vaccine development, told Health.

The only way for vaccine shedding to potentially happen is from a live attenuated vaccine, which means it contains a weakened version of a germ that causes a disease. These vaccines work by letting the virus replicate inside a person's body enough to stimulate an immune response, but not enough to cause the (influenza) disease itself, per the Centers for Disease Control and Prevention (CDC). The live-attenuated vaccines currently used for routine vaccinations in the US include:

  • MMR (measles, mumps, and rubella)
  • Chickenpox
  • Rotavirus
  • Nasal flu spray (influenza)

And while this type of vaccine can cause a person to shed the weakened virus (often through their feces), it's extremely rare to spread enough of the germ to infect someone else with the disease.

Take the flu vaccines, for example. While researchers have discovered cases in which the weakened flu virus is transmitted from a vaccinated person to someone else, they've found no instances of that causing serious illness. Likewise, since 1995, the CDC has only reported eleven cases of healthy vaccinated people (all of whom developed a rash after their vaccine) spreading the weakened virus used in the chickenpox shot to unvaccinated people around the world.

"There are other vaccines that have been investigated that could lead to this. For example, there was [the oral] polio vaccine that had a few cases of reported viral shedding, but it's not used in the US anymore," explained Venditto.

Can COVID-19 Vaccines Cause Shedding?

As of May 2022, none of the COVID-19 vaccines approved in the United States contain a live or weakened version of the virus. For this reason, there is no chance of vaccine shedding from the COVID-19 vaccine candidates.

You have two types of COVID-19 vaccines used in the United States to choose from. The first is messenger RNA (mRNA)-based vaccines, the type used by Pfizer-BioNTech and Moderna. Both mRNA vaccines teach our immune cells to create the "spike protein" found on the surface of SARS-CoV-2.

"Your body recognizes that protein as an enemy, then your body makes antibodies for that protein," Aaron E. Glatt, MD, chair of medicine at Mount Sinai South Nassau and spokesperson for the Infectious Diseases Society of America, told Health. "The mRNA vaccines don't give you any virus at all."

The mRNA used in these vaccines doesn't cause any sort of infection, and even if they could, they don't stick around long enough to pose much of a risk. By their very nature, mRNA molecules are fragile and degrade quickly (that's why super cold temperatures are used to preserve them). According to the American Medical Association (AMA), the mRNA vanishes from the body within 24 hours, and the spike protein it helps cells produce clears out within 72 hours.

Then you've got the Johnson & Johnson COVID-19 vaccine. That one is a viral vector vaccine. According to the CDC, the Johnson & Johnson vaccine works similarly to the Pfizer-BioNTech and Moderna vaccines because it uses the body's cells to create that spike protein, which the immune system then learns how to attack. The difference is that the Johnson & Johnson shot delivers the instruction manual through another virus, rather than mRNA. That virus is an adenovirus, not the coronavirus that causes COVID-19, and scientists have modified it not to replicate or cause illness.

So even though vaccine virus shedding is a potential (yet extremely rare) risk with live attenuated vaccines, it doesn't apply to these vaccines since they don't contain the virus that causes COVID-19.

"In medicine, we don't say 'zero' too often, but there is zero chance for the COVID-19 vaccines to cause you to shed the virus," said Dr. Glatt.

Where To Find Reliable Vaccine Info Online

While vaccine shedding myths —as well as other misconceptions about the COVID-19 shots— are easily debunked, they spread like wildfire online, threatening public health and efforts to smother the coronavirus.

Case in point: In October 2021, a private school in Miami required students who received the COVID-19 vaccine to stay home for at least 30 days, citing false claims about vaccine shedding. In April 2021, the same school used the same reason to bar vaccinated teachers from having contact with students. Parents of students needed to choose between getting the vaccine and having their child fall behind or risk their child contracting a COVID-19 infection.

"This is really one of the tools in the anti-vax arsenal of storylines that are rolled out to discourage people from getting vaccinated," said Venditto. "If people don't know what's actually happening and the science going into this, you hear this stuff, and you might actually believe it."

Hence why it's so important to be careful to look into any weird claims you see online before believing them, let alone sharing the info with others. Here are a few places where you can find reliable health information online:

Many other websites that end in .edu or .org can be trustworthy too, but it's worth looking into the organizations running any site to make sure it's a quality source.

As for the information you see on social media, experts advise proceeding with caution. "Even if the person has a huge following, that doesn't mean they're qualified to provide trustworthy advice on health and medicine," said Dr. Glatt.

"You wouldn't want me to play baseball for the New York Yankees, and you wouldn't want a sports professional playing doctor," described Dr. Glatt.

Finally, don't hesitate to get in touch with your doctor if you have concerns about the COVID-19 vaccines, or anything else related to your health. They have your best interest in mind and are often the best source of personalized advice for your situation.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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