Should you vaccinate your kids if they have the MTHFR mutation?

You may have read or heard that anyone who carries MTHFR variants should not be vaccinated. Usually, the reason given is that those with decreased MTHFR enzyme activity cannot detoxify or ‘handle’ vaccinations, often with references to mercury in the vaccines.

This article reviews the published scientific studies on the topic of MTHFR and vaccinations.

MTHFR Gene and Vaccinations:

The MTHFR gene codes for the enzyme that plays a critical role in using folate in the methylation cycle. There are two genetic variants of MTHFR that many researchers have focused on. These two variants are known as C677T and A1298C. (Read more and check your genetic raw data here: How to check your genetic data for MTHFR.)

I purposefully refer to the genetic change in MTHFR as a variant instead of a mutation.

At least one copy of the C677T variant is found in over half the people in most population groups. This is not a rare mutation, but rather a common variant that causes a change in how the gene functions.

Studies on the MTHFR gene and vaccines:

Researching the studies on MTHFR variants and vaccination injuries or adverse events lead me to exactly one study.  Seriously. One study — on a vaccine that is no longer given.

It is an open-access article on genetic variants and adverse reactions to the smallpox vaccine.

Overview of the study: In a study conducted by Vanderbilt University, 131 people (average age of 23) received a vaccine for smallpox. The results showed that those individuals with an MTHFR C677T variant were more likely to have an adverse reaction to the vaccination. The study also linked other genes to an increase in adverse events.

Adverse events were defined as a skin reaction at the site of injection, fever within 30 days of the vaccine, or enlarged or tender lymph nodes.  40 study participants reacted to the vaccine and 69 participants did not. [ref] Smallpox vaccines have not been used on the general public in the US in over 46 years, and none of the study participants had previously received a smallpox vaccine. The vaccine contains a live virus that is similar to smallpox. It is given only to those who are at risk of smallpox exposure. [ref]

Update! Read why the author of that study does NOT think it shows a reason not to vaccinate: article in The Atlantic.

What about studies on MTHFR and vaccine excipients?

Some claim that excipients added to vaccines are the reason that MTHFR C677T variant carriers should not be vaccinated.

There was a small study done showing that people with the MTHFR C677T variant might be more sensitive to mercury. The study looked at the genes of 25 participants that had been diagnosed as sensitive to mercury compared with a control group of 25. The MTHFR 1298C/C genotype was more common in the mercury-sensitive group. (Note that the study had a very small group size!)

But…   Mercury has been removed from children’s vaccinations since 2001 in the U.S.  Seasonal flu vaccines for those over 6 years old can still contain mercury, so check the ingredients on that particular vaccine if you are concerned about mercury.

I found no other links between MTHFR variants and other common excipients in vaccines. [ref]

A study on vaccines and MTHFR that (hopefully!) doesn’t apply to children found that a cocaine vaccine actually worked better for people with the MTHFR 677 T/T genotype (decreased cocaine use and depression scores). [ref]

Coverup conspiracy?

The ‘conspiracy theorist’ in the back of my mind wondered if the link between MTHFR and vaccine injuries was just being covered up — or perhaps deliberately not studied.

But… that doesn’t seem to be the case.

There are quite a few studies that look at the interaction between genetics and vaccination reactions. The studies cover how different genetic variants increase or decrease the effectiveness of vaccines as well as how genes interact with adverse events.

One study found quite a few HLA (human leukocyte antigen) gene variants as well as other immune system gene variants that do play a role in how vaccines work. The study examined the response to measles vaccinations and found that HLA type predicted whether the recipient would have a strong or weak immune response to the vaccine. [ref] Another study found that CD46 genetic variants also influenced the response to the measles vaccine. [ref]

These immune system genes make sense to influence vaccine response — a lot more sense than the MTHFR variant. So instead of a conspiracy, it may be more the case that studying the MTHFR variant in conjunction with vaccines just doesn’t make a lot of sense.

Summing up the evidence:

  • No scientific evidence pointing to the common MTHFR variants playing a role in vaccination adverse events.
  • Carriers of the MTHFR C677T T/T genotype are possibly more likely to react mildly to the type of smallpox vaccine that was used over 10 years ago.
  • Other genetic variants have been found to increase the risk of either adverse events or vaccine effectiveness — and it makes more sense to study those genes in conjunction with vaccination reactions.

Related Genes and Topics:


Wondering why your neurotransmitters are out of balance? It could be due to your COMT genetic variants. The COMT gene codes for the enzyme catechol-O-methyltransferase which breaks down (metabolizes) the neurotransmitters dopamine, epinephrine, and norepinephrine.


Migraine plague more than a billion people worldwide. That is a lot of people who know the pain, mental fogginess, sensitivity to light, and overwhelming desire to crawl into a dark hole and hide from the world. Knowing how your genes influence your risk of migraines can help you tailor solutions that may work better for you.

Initially published July 2017, updated Jan 2020.


Austin, David William, et al. “Genetic Variation Associated with Hypersensitivity to Mercury.” Toxicology International, vol. 21, no. 3, Dec. 2014, pp. 236–41. PubMed, doi:10.4103/0971-6580.155327.
Clifford, Holly D., et al. “CD46 Measles Virus Receptor Polymorphisms Influence Receptor Protein Expression and Primary Measles Vaccine Responses in Naive Australian Children.” Clinical and Vaccine Immunology: CVI, vol. 19, no. 5, May 2012, pp. 704–10. PubMed, doi:10.1128/CVI.05652-11.
Felger, J. C., and F. E. Lotrich. “Inflammatory Cytokines in Depression: Neurobiological Mechanisms and Therapeutic Implications.” Neuroscience, vol. 246, Aug. 2013, pp. 199–229. ScienceDirect, doi:10.1016/j.neuroscience.2013.04.060.
Haralambieva, Iana H., et al. “The Genetic Basis for Interindividual Immune Response Variation to Measles Vaccine: New Understanding and New Vaccine Approaches.” Expert Review of Vaccines, vol. 12, no. 1, Jan. 2013, pp. 57–70. PubMed Central, doi:10.1586/erv.12.134.
Reif, David M., et al. “Genetic Basis for Adverse Events after Smallpox Vaccination.” The Journal of Infectious Diseases, vol. 198, no. 1, July 2008, pp. 16–22., doi:10.1086/588670.
—. “Genetic Basis for Adverse Events Following Smallpox Vaccination.” The Journal of Infectious Diseases, vol. 198, no. 1, July 2008, pp. 16–22. PubMed Central, doi:10.1086/588670.
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Vaccines: Vac-Gen/Additives in Vaccines Fact Sheet. 14 Jan. 2020,
Zhang, Sarah. “Why Anti-Vax Doctors Are Ordering 23andMe Tests.” The Atlantic, 23 May 2019,

Author Information:   Debbie Moon
Debbie Moon is the founder of Genetic Lifehacks. She holds a Master of Science in Biological Sciences from Clemson University and an undergraduate degree in engineering. Debbie is a science communicator who is passionate about explaining evidence-based health information. Her goal with Genetic Lifehacks is to bridge the gap between the research hidden in scientific journals and everyone's ability to use that information. To contact Debbie, visit the contact page.