COVID‑19 Vaccines Cannot "Shed"

Nurse's Blog, statdate 2021.07.21

In the interest of full disclosure, let me begin by saying that I am not an epidemiologist, immunologist, or a virologist. What I am is a concerned nurse who wants to help make reliable information easier to find and understand. As a nurse, my education has included relevant topics such as disease prevention, pathophysiology, microbiology, and pharmacology. This is a blog. Information found here is generalized and should not be used as a substitute for medical advice; please consult your personal healthcare provider before acting on any information shown here.

All information here is, to the best of my knowledge, current as of the date this page was written (date under the title of this page). This page may be updated as I find new information. A complete list of cited references is included at the end of this page.

Rumors of Vaccine Shedding

Rumors of vaccine shedding have been spreading lately surrounding the COVID‑19 vaccines, claiming that simply being near a vaccinated person can cause an unvaccinated person to experience vaccine side effects. While vaccine shedding is a real phenomenon, it is rare and only occurs with live inoculation or attenuated vaccine administration; the COVID‑19 vaccines authorized for use in the United States do not fall into either category. This post is intended to define relevant terms, discuss the history of vaccination, and ultimately dispel this rumor.

Important Definitions

Vaccine Shedding: A phenomenon where a person (or other organism) becomes infected by a pathogen contained in an inoculation/vaccine and has the possibility of spreading it to others. Vaccine shedding gets its name from a process known as viral shedding.

Viral Shedding: When a person (or other organism) becomes infected by a virus, that virus "hijacks" the person's cells in order to replicate and spread. When replicated viruses spread from person to person, it is referred to as shedding.

Live Inoculation: Intentional exposure to a virus with the intent of developing immunity following infection. This act dates back hundreds of years, at least, but is no longer practiced due to modern vaccines being significantly safer.

The Origins of Vaccination

There are historical records of live inoculations dating back to at least the fifteenth century, where people would intentionally breathe in the dried scabs of someone with smallpox. Although crude, this practice was found to be safer than natural smallpox infection. Natural smallpox infection had approximately a 30% chance of death, whereas the fatality rate with live inoculation was less than 5%.

It was realized in the late 1700s that farmers and milkmaids who had previously contracted cowpox had no reaction to live smallpox inoculation. Upon further investigation, it was discovered that these people rarely contracted smallpox when exposed to someone else who was infected. As cowpox infection is typically mild, a vaccine was derived from the udders of infected cows or the legions of infected individuals. The term "vaccine" was coined from this process, based on the Latin word for cow, vacca.

More Definitions

Replication Competence: The ability of a virus to replicate. Viruses found in nature are generally replication competent. Most vaccines used today do not contain replication competent viruses and are therefore incapable of shedding.

Attenuated Vaccine: Attenuated vaccines contain a form of virus that has been weakened to prevent it from infecting the recipient. Most commonly, the virus is one that was classically able to infect the recipient, but has been trained to only be able to infect another species. The virus contained in this type of vaccine is still alive, but a healthy immune system will destroy the virus before it has the opportunity to learn to infect the recipient. Examples include the MMR vaccine, chickenpox vaccine, and some flu vaccines.

Inactivated Vaccine: Also know as "killed virus vaccines," inactivated vaccines contain a whole virus that has been treated with heat or a chemical to kill it. It is essentially the "skeleton" of the original virus. The recipient's immune system should be able to develop immunity without risk of becoming infected. Examples include the hepatitis A vaccine, rabies vaccine, and most flu vaccines.

Subunit Vaccine: These vaccines only contain a fragment of a virus, such as its shell. The hepatitis B vaccine is a subunit vaccine.

Viral Vector Vaccine: Viral vector vaccines are related to subunit vaccines, but the target subunit is delivered by a live virus that is typically replication incompetent. The Johnson & Johnson/Janssen COVID‑19 vaccine is a viral vector vaccine that uses a replication incompetent virus to deliver a portion of the virus that causes COVID‑19 (SARS‑CoV‑2).

mRNA Vaccine: mRNA vaccines contain no virus or viral fragment at all. Instead, they contain a strand of genetic material that serves as an "instruction manual" to temporarily teach your cells how to make a viral subunit, then act as a subunit vaccine would act. This type of vaccine is the safest type of vaccine currently in use, as manufacturers and vaccine recipients are never exposed to the target virus. Examples include the Pfizer-BioNTech and Moderna COVID‑19 vaccines.

Modern Day Vaccination

The science of vaccination has improved drastically from its early days. The majority of today's vaccines are replication incompetent, meaning there is zero risk of the recipient of those vaccines becoming ill or spreading what they are supposed to be getting vaccinated against. Because of vaccines, smallpox has been eradicated from the world, polio is almost unheard of, the need for liver transplants caused by hepatitis has gone down, and rates of cervical, anal, and throat cancers are decreasing. With children being vaccinated against chickenpox rather than going to "pox parties" to contract the disease, it is very likely that they will never experience the pain of shingles when they grow old.

Vaccine shedding was possible in the days of live inoculations, but those days are behind us. It is theoretically possible with attenuated vaccines, but is extremely rare with the exception of the oral poliovirus vaccine, which has been replaced with an inactivated vaccine in most parts of the world.

The belief that vaccine shedding could happen with the COVID‑19 vaccines being used in the United States is unfounded. mRNA vaccines contain no virus, making shedding completely impossible. While the Johnson & Johnson/Janssen COVID‑19 vaccine is a viral vector vaccine utilizing a live virus to deliver a viral subunit, the virus utilized is a genetically engineered virus that contains zero capability of replicating in any species, making it as harmless as an inactivated vaccine.

REMINDER: Information found here is generalized and should not be used as a substitute for medical advice; please consult your personal healthcare provider before acting on any information shown here.


Altamirano, J., Sarnquist, C., Behl, R., García-García, L., Ferreyra-Reyes, L., Leary, S., & Maldonado, Y. (2018). OPV vaccination and shedding patterns in Mexican and US children. Clinical infectious diseases: An official publication of the Infectious Diseases Society of America, 67(suppl_1), S85–S89.

Boylston A. (2013). The origins of vaccination: Myths and reality. Journal of the Royal Society of Medicine, 106(9), 351–354.

Centers for Disease Control and Prevention. (2021). History of smallpox.

The Children's Hospital of Philadelphia. (2021, June 3). Feature article: viral shedding and COVID-19 - what can and can't happen.