COVID-19 Vaccine Shedding—Why Vaccine Shedding Won't Happen

None of the COVID-19 vaccines approved in the United States cause vaccine shedding.

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A COVID-19 vaccine can provide peace of mind and lessen the fear of getting sick when traveling, eating in a crowded restaurant, and safely hugging relatives. Per the Centers for Disease Control and Prevention (CDC), while no vaccine is 100% effective, the COVID vaccine provides protection against severe disease, hospitalization, and death from the COVID virus.

However, in April 2021, a Canadian news outlet, Global News, ran a story about how one store in Canada banned vaccinated customers from entering. The reason? According to the owner, people who had received a COVID vaccine could "shed" the virus to others and cause harm.

Let's clear this myth up. The CDC lists the possible side effects of COVID vaccines. Vaccine shedding is not one of the documented side effects. Additionally, the CDC addressed this myth directly and stated this is not a risk with any available COVID vaccines.

However, despite the facts about COVID vaccines, misconceptions that they cause "vaccine shedding" still circulated, possibly contributing to fear and hesitancy regarding the vaccine.

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

What Is 'Vaccine Shedding'?

Like many myths, the belief that interacting with someone who got a vaccine might be harmful 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, said to Health.

The CDC provides an overview of the COVID vaccines available and the basis of each of the vaccines. The Moderna and Pfizer vaccines utilize mRNA technology. Novavax utilizes a protein subunit, and Johnson & Johnson Janssen's vaccine is a viral vector vaccine. None of the currently available vaccines utilize a weakened virus as the base for the vaccine.

How Does Vaccine Shedding Happen?

The only way vaccine shedding occurs is from a live attenuated vaccine, which means the vaccine contains a weakened version of the virus 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 disease itself, per the CDC. The CDC explained 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—it's extremely rare to infect someone else with the disease. A study published in 2018 in the journal Human Vaccines and Immunotherapeutics explained why the live attenuated influenza vaccines (LAIV) are generally safe.

Per the study, even if someone receives a LAIV and sheds the influenza virus, the virus they are shedding is likely not the wild type of the virus—meaning the strain circulating in the public. LAIV are created to provoke an immune response against the theorized dominant influenza strains to keep you healthy.

However, the study explained that if someone were to become infected with the influenza virus naturally (i.e. the wild type) shortly after being vaccinated, this could result in the possibility of shedding a version of the influenza virus that could be spread to others. This is generally unlikely, and considered rare.

In fact, the CDC, referenced a study conducted in a childcare setting and published in the Pediatric Infectious Disease Journal in 2006. While an older study, it is a randomized, double-blind study—meaning it is the gold standard of studies.

In this study, 98 children received a live attenuated influenza vaccine, and 99 received a placebo vaccine. One of the 99 children who received the placebo became infected with an influenza strain due to vaccine shedding from children in the live vaccine group. However, the child who became sick only had symptoms of a mild upper respiratory infection, not a severe form of the disease.

While researchers have discovered cases in which the weakened flu virus is transmitted from a vaccinated person to someone else (when live-attenuated vaccines are used), they've found no instances of the shedding causing severe illness, according to the CDC,

Likewise, the varicella (chickenpox) vaccine is another commonly used live attenuated vaccine. Since 1995, the CDC has only reported eleven cases of healthy vaccinated people spreading the weakened virus used in the chickenpox shot to unvaccinated people.

The takeaway is that viral shedding after a vaccine is only possible when live attenuated vaccines are used. Additionally, it is incredibly rare that this leads to disease in others. Overall, live attenuated vaccines are generally safe and pose minimal risk. The main exceptions are in individuals who are immunocompromised and those who are pregnant, per MedlinePlus.

What Is mRNA Vaccine Technology?

When the mRNA vaccines were developed, there was the misconception this was a new vaccine technology. The vaccines were met with apprehension by many in the public. However, according to an article published by the journal Nature, research on how to deliver mRNA into cells began back in the 1970s.

Per MedlinePlus, mRNA stands for messenger RNA. In the cells of our bodies, mRNA codes for various proteins. Once the protein is made, the mRNA is broken down quickly and does not enter the nucleus of the cell of alter the body's DNA.

The COVID mRNA vaccines were not the first mRNA vaccines developed. There was already one in use for the Ebola virus. However, because that virus is limited to a small number of African countries, there was no large-scale commercial development of the vaccine, per the CDC.

The CDC explained that with mRNA vaccines, the vaccines trigger the body to produce a protein that causes an immune response in our bodies. Antibody production is part of this immune response. These antibodies protect you if you are exposed to the germ or virus.

Regarding the mRNA vaccines, "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, said to Health. "The mRNA vaccines don't give you any virus at all."

The mRNA used in these vaccines doesn't cause any infection; even if it could, it doesn't stick around long enough to pose much of a risk. A Pharmaceutics article explained the fragility of mRNA was one of the biggest challenges with mRNA vaccine technology. Per MedlinePlus, mRNA molecules degrade quickly.

Can Any COVID-19 Vaccines Cause Shedding?

The short answer is no, none of the COVID vaccines cause shedding. The Johnson & Johnson Janssen COVID vaccine, which uses a viral vector vaccine. According to the CDC, the Johnson & Johnson Janssen vaccine works similarly to the Pfizer-BioNTech and Moderna vaccines.

This vaccine also uses the body's cells to create the spike protein, which the immune system then learns how to attack. The spike protein is the part of the COVID virus that can make you sick, per the CDC. So, per the CDC, if the body recognizes the spike protein from COVID as a threat, it can build up a response to be able to protect you from the actual spike protein on the COVID virus.

The difference is that this vaccine delivers the instruction manual through another virus (an adenovirus) rather than mRNA. Scientists have modified the adenovirus not to replicate or cause illness.

The American Society of Gene and Cell Therapy (ASGTC) explained adenoviruses are typically the cause of common illnesses that cause symptoms such as fevers and coughs. However, per the ASGCT scientists have utilized vaccine technology to be able to use these viruses to carry genes to a cell without making the individual sick. The part of the adenovirus that causes illness in adenovirus based vaccines is deactivated.

In the case of adenovirus based COVID vaccines, per the ASGTC, these genes code for the COVID spike protein. This allows the individual's body to recognize the spike protein as an invader and build an immune response.

In contrast, while the two available mRNA vaccines (Pfizer and Moderna) and the Johnson & Johnson Janssen vaccine all stimulate the body to generate the spike protein from the COVID virus, Yale Medicine explained the Novavax vaccine works by directly injecting a version of the COVID spike protein into the body, along with an immune stimulant.

The spike protein that is injected does not contain any live virus. Instead, it utilizes a version of the spike protein generated in a lab through nanoparticulate technology—meaning a tiny particulate is used.

Per Yale Medicine, the technology behind Novavax is also seen in many other common vaccines. These include shingles, human papillomavirus (HPV), and the DTaP (diphtheria, tetanus, and pertussis) vaccines.

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 live virus that causes COVID

"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, and backed up by the CDC.

Where To Find Reliable Vaccine Info Online

While vaccine-shedding myths—as well as other misconceptions about the COVID vaccines—are easily debunked, they spread like wildfire online, threatening public health and efforts to prevent the spread of the COVID virus.

Case in point: In October 2021, NBC News ran a story about a private school in Miami that required students who received the COVID vaccine to stay home for at least 30 days. The school cited false claims about vaccine shedding. In April 2021, the school also used the same reason to ban vaccinated teachers from having contact with students.

As a result, parents of students needed to choose between getting the vaccine and having their child fall behind or not vaccinating them and risk their child contracting a COVID 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 suspicious 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:

As for the information you see on social media, experts advise proceeding cautiously. "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.

It's important to obtain information from someone who is an expert in their field. For example, Dr. Glatt said, "you wouldn't want me to play baseball for the New York Yankees, and you wouldn't want a sports professional playing doctor."

A Quick Review

Overall, while there are different COVID technologies, none of the vaccines used against the COVID virus utilize attenuated live vaccine technology. For this reason, vaccine shedding won't happen with any of the COVID vaccines.

And, finally, don't hesitate to contact a healthcare provider if you have concerns about the COVID vaccines or anything else related to your health. They 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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