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What do we know about the toxicity of spike proteins made from COVID-19 vaccines?


by Health Desk | Published on June 7, 2021 – Updated on October 21, 2022 | Explainer

Summary: There is currently no scientific evidence available that suggests that spike proteins created in our bodies from the COVID-19 vaccines are toxic or damaging to the human body, as is being claimed on some social platforms.

What our experts say

The spike proteins produced in the body from COVID-19 vaccination are widely considered safe, whether from mRNA vaccines (e.g., Moderna, Pfizer) or viral vector vaccines (e.g., AstraZeneca, Johnson & Johnson). These spike proteins from COVID-19 vaccination play an important role in training the immune system to protect the body from COVID-19.

False claims about the toxicity of spike proteins from COVID-19 vaccination often come from the misinterpretation of studies, and fail to take into account how spike proteins from COVID-19 vaccination behave differently than the spike proteins from natural COVID-19 infection.
One of the false claims about the harms of spike proteins is that they can damage the body’s DNA repair mechanisms (a set of processes through which a cell can correct damage to DNA molecules). There is no evidence that mRNA vaccines or the spike proteins produced by those vaccines in the human body can interfere with DNA repair mechanisms.

One study published in 2021 made this claim that continues to be referenced. The study was retracted later in the same year due to concerns about invalid methods. The idea that vaccines could affect DNA repair is concerning because sustained, constant damage to DNA can lead to development of cancers. There is no evidence that mRNA vaccines or the spike proteins produced by them in the body can affect our body’s DNA in that way or cause cancer. In contrast, researchers and scientists are hopeful that mRNA technology can be used to treat and prevent cancer. Researchers at both Pfizer-BioNTech and Moderna were working on mRNA vaccines for cancer before the COVID-19 pandemic and were able to use the experience they had with the technology to develop the mRNA COVID-19 vaccines that are available today.

A second false claim about the harms of spike proteins is that they can affect women’s fertility. More specifically, these claims state that COVID-19 spike proteins can cause a woman’s immune system to attack a different type of spike protein that is essential for placental health during pregnancy. Research has proven that these are two completely different proteins. mRNA vaccines are safe to get during pregnancy, and scientists, researchers, and doctors recommend that pregnant people get vaccinated against COVID-19 as soon as they are eligible.

A third misleading claim about spike proteins produced as a result of vaccines is that they travel in our bloodstreams. Research shows that spike proteins produced as a result of COVID-19 vaccines primarily stay stuck to the surface of the cells around the vaccine's injection site, and are not known to wander around to other parts of the body. This is because spike proteins have a transmembrane anchor region that leaves it stuck to the surface of the cell where it was produced (by the muscle in the injection site). While traveling through the bloodstream, there is no evidence of spike proteins generated by vaccines causing harm.

A very tiny dose of the vaccine does make it to the bloodstream (about 1%), but is destroyed completely once it reaches the liver by the enzymes there. These concerns about the spike proteins produced from COVID-19 vaccines have been addressed by major public health entities. The U.S. CDC, for instance, refers to the spike protein made from the vaccine as harmless.

Vaccines go through very rigorous evaluation using standards set by governments and international agencies – including the U.S. FDA and the World Health Organization – to meet safety and efficacy criteria. When the mRNA vaccines for COVID-19 were first developed, thousands of people underwent clinical trials over several months to understand if there were any side effects or risks associated with the vaccines. Currently, in the U.S. alone, more than 265 million people have received at least one dose of a vaccine against COVID-19. Including both first and second doses and boosters, more than 608 million doses of mRNA vaccines have been given in the country.

There is no scientific evidence available that suggests that spike proteins created in our bodies from the COVID-19 vaccines are toxic or damaging. The COVID-19 vaccines, however, are relatively new. As a result, long-term side effects and reasoning for any side effects are not yet fully known. The vaccines are still being monitored for any safety concerns or patterns being seen that can risk human well-being.

Several systems help us monitor vaccine safety. In the United States, these include the Vaccine Adverse Event Reporting System (VAERS), The Vaccine Safety Datalink (VSD), the Post-License Rapid Immunization Safety Monitoring (PRISM), and the Clinical Immunization Safety Assessment Project (CISA). Similarly, the World Health Organization, European Union, and other countries and regions have independent oversight mechanisms. These teams and systems are used to monitor side effects and any other patterns of risks from vaccines.

Context and background

The human immune system has the ability to remember dangerous infections that it is exposed to; meaning that after the first time it encounters a threat, the second time the immune response will be faster, stronger and more effective in defending the body. This is the principle that guides immunization with vaccines, and it is called acquired immunity.

There are two general vaccine types for COVID-19 available according to the U.S. CDC: protein subunit vaccines and mRNA vaccines.

Protein Subunit vaccines contain some pieces of viral protein along with another component that helps the body respond to it. These pieces of viral protein are spike proteins. Spike proteins are an important component in some vaccines as they can familiarize the body’s immune system with these proteins and allow them to be able to target and respond quickly to the spike proteins of the actual virus when infected. This response is how the body protects itself against COVID-19.

mRNA vaccines work slightly differently. mRNA, short for messenger RNA, is a type of genetic material that carries information (or code) for a specific type of protein. In essence, it contains information that functions as a “recipe” that the body can understand and use to create this special protein. mRNA exists in human cells as an instrument of moving information inside the cell and maintaining cell functions that are essential for life. When the mRNA of a virus is introduced into a human cell, it takes over the cell’s control center and makes proteins that help the virus to multiply in our bodies, thus causing disease. mRNA vaccines use this process to allow the body to produce a small amount of spike proteins that are harmless to the body. However, the spike proteins produced teach the immune system to recognize the virus, and prepare the body to respond to the actual virus when exposed to it.

Vaccine development, approval, and manufacturing involve rigorous processes, first among which is safety. Only if a vaccine is considered safe and effective, and only if the benefits outweigh the risks, is a vaccine authorized for use. Several scientists and experts at regulatory agencies like the U.S. FDA and World Health Organization study vaccine data. These experts evaluate vaccine safety and efficacy before deciding whether it's safe for the public to use.


  1. mRNA Vaccines  (U.S. CDC)
  2. Spike Protein (Science Direct)
  3. Explainer: What is a spike protein? (Science News for students)
  4. Spike Protein/ S Protein (SinoBiological)
  5. Structure, Function, and Antigenicity of the SARS-CoV-2 Spike Glycoprotein (Cell)
  6. Development and Licensure of Vaccines to Prevent COVID-19 - Guidance for Industry (US FDA)
  7. Spike Protein Behavior (Science Translational Medicine)
  8. Possibility of COVID-19 Illness After Vaccination (U.S. CDC)
  9. COVID-19 Breakthrough Case Investigations and Reporting(U.S. CDC)
  10. Ensuring the Safety of Vaccines in the United States (U.S. CDC)
  11. Ensuring the Safety of Vaccines in the United States (US FDA)
  12. Vaccine Safety Monitoring (US CDC)
  13. Vaccine Safety Basics (WHO)
  14. Can mRNA Vaccines Help Treat Cancer? (NIH: National Cancer Institute)
  15. COVID-19 Vaccines: Myth Versus Fact (Johns Hopkins Medicine)
  16. Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons (New England Journal of Medicine)
  17. COVID-19 Vaccination Considerations for Obstetric–Gynecologic Care (The American College of Obstetrics and Gynecology)
  18. Retraction: Jiang, H.; Mei, Y.-F. SARS-CoV-2 Spike Impairs DNA Damage Repair and Inhibits V(D)J Recombination In Vitro. Viruses 2021, 13, 2056 (PubMed)
  19. Coronavirus Vaccines and Cancer (Science)
  20. COVID-19 Vaccinations in the United States (U.S. CDC)
  21. Vaccines and Immunization: Vaccine Safety (WHO)

Spike Protein Behavior (Science)

Used with Permission from Health Desk, a public health hub that explains emerging COVID-19 science.

This article was written and edited by the Tayo editorial desk and has been reviewed by an independent panel of subject matter experts.

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