Should Parents Be Worried About Vaccine Shedding?

Vaccine shedding refers to the release of a weakened vaccine virus from the body after receiving certain live attenuated vaccines.

If you've spent any time online, you've probably seen the term vaccine shedding. Some posts claim that recently vaccinated people—especially kids—can spread vaccine ingredients or even make others sick. It's an alarming idea, particularly for families with newborns or loved ones who have weakened immune systems.

While vaccine shedding is a real phenomenon with a small number of vaccines, it's often misunderstood. In most cases, it's not something parents need to worry about. Understanding which vaccines can shed, how shedding occurs, and who—if anyone—should take extra precautions can help separate fact from fiction.

In this article, we'll explain what vaccine shedding is, which vaccines may shed, who should be cautious around recently vaccinated individuals, and why COVID-19 vaccines cannot cause vaccine shedding.

What Is Vaccine Shedding?

Vaccine shedding refers to the release of a weakened vaccine virus from the body after receiving certain live attenuated vaccines (1,2). These vaccines contain a live virus that has been weakened so it can stimulate an immune response without causing the full illness in healthy people (1,2).

When you’re vaccinated, your immune system learns to recognize the weakened version of the virus and creates the antibodies it needs to fight off future infections. It also builds immune memory, which allows your body to respond and recognize that virus quicker in the event of exposure (2).

Because live attenuated vaccines briefly replicate in the body to produce this immune response, small amounts of the weakened virus may be present in certain bodily fluids for a short period of time (1). This process of temporary release is what’s known as vaccine shedding.

Vaccine shedding is different from shedding during a naturally occurring infection. The viruses used in vaccines are significantly weakened, making it much less likely for them to spread or cause illness than a wild virus (2).

Most routine vaccines—including inactivated vaccines, protein-based vaccines, and mRNA vaccines—can’t shed because they don’t contain live viruses (1).

For more information on vaccines, see this article: Vaccine Schedules

Which Vaccines Shed?

Rotavirus

Shedding occurs in stool
Sheds up to 1-2 weeks after vaccination (3)

For more information on rotavirus: Rotavirus

Live Attenuated Influenza (Nasal Spray)

Shedding occurs in nasal secretions
Sheds up to 7 days after vaccination (4)

Varicella (Chickenpox)

Rarely sheds
Shedding occurs in fluids from vaccine-related rash (if one develops)
Sheds until rash resolves (5)

For more information on varicella: Varicella (Chickenpox)

Although the measles, mumps, rubella, and varicella (MMRV) vaccine contains live attenuated viruses, transmission of vaccine virus is extremely uncommon (5,6). In the case of the varicella vaccine, transmission has only been documented in rare instances when a vaccinated person develops a rash after vaccination (5,6).

For most healthy children and adults, vaccine shedding doesn’t pose a meaningful risk (5,6).

A man washes his hands thoroughly with soap.

Who Should Take Extra Precautions Around the Recently Vaccinated?

Most families don't need to change their daily routines after a child receives a live vaccine (5). However, a few temporary precautions may be recommended for people with severely compromised immune systems, such as those undergoing chemotherapy, recent organ transplant recipients, or individuals with certain inherited immune deficiencies (5).

Because rotavirus vaccine virus can be shed in stool, caregivers should wash their hands thoroughly after changing diapers for several weeks following vaccination (3,5). If a child develops the uncommon rash that can occur after receiving the varicella vaccine, people with severely weakened immune systems should avoid direct contact with the rash until it has completely cleared up (5).

Outside of these situations, transmission of vaccine viruses is rare (6). If you or someone in your household has a weakened immune system, your healthcare provider can recommend any additional precautions that may be appropriate based on individual needs (5).

For more information on what to do when you’re exposed to a sick person: What to Do After Exposure to a Sick Person: Immune Support Tips for Families

What About COVID-19 Vaccine Shedding?

The COVID-19 vaccines used in the United States do not contain live coronavirus (7). Instead, mRNA vaccines provide instructions that allow your cells to temporarily produce a harmless version of the virus's spike protein (7,8). This helps your immune system recognize the virus and build defenses against future infection (7,8).

The spike protein produced after vaccination is not an infectious virus—so, it cannot reproduce, spread to other people, or cause someone else to develop COVID-19 (7,8). After stimulating an immune response, your body quickly breaks down the spike protein and the vaccine's mRNA.

Because COVID-19 vaccines do not contain a live virus, they cannot cause vaccine shedding (7,8).

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Summary

Vaccine shedding is a real but uncommon phenomenon that only occurs with certain live attenuated vaccines (1,2,5,6). Even when shedding does occur, transmission to other people is rare, and healthy individuals generally do not need to take special precautions.

For families with someone who has a severely weakened immune system, simple measures—such as careful handwashing after changing the diaper of a recently vaccinated infant or avoiding contact with a vaccine-related chickenpox rash—may be recommended (3,5).

COVID-19 vaccines are different. Because they do not contain a live virus, they cannot shed or spread COVID-19 to others (7,8).

If you have questions about vaccines or whether additional precautions are needed for someone in your household, talk with your healthcare provider. They can help you make decisions based on your family's individual health needs and the latest immunization recommendations.