MTHFR and VaccinesI recently read, for the million-teenth time, that anyone with MTHFR variants should not be vaccinated.  The argument always seems to be that those with decreased MTHFR enzyme activity cannot detoxify or handle a vaccination. This seems to be accepted as fact by some, but I hadn’t really read anything other than anecdotes about it.  So I decided to look into the scientific studies on the topic.

**Note that I’m not weighing in on whether or not kids should be vaccinated on the currently advised pediatric vaccination schedule — just addressing the science behind MTHFR variants causing adverse reactions to vaccines **

Looking into the studies on MTHFR variants and vaccination injuries and/or adverse events lead me to exactly one study.  The study was small, with less than 200 people included in it.  It looked at several different variants as related to adverse events from a smallpox vaccination.  It did find that those individuals with an MTHFR C677T variant were more likely to have an adverse event.  It also linked a couple of other variants with an even greater likelihood of adverse events.   Again, though, this is a small study using a vaccination that is not normally in use today.  (Smallpox vaccines have not been used on the general public in the US for about 45 years.)

Could there be other studies on MTHFR and vaccination adverse events?  Possibly, but I couldn’t find any that have been published.  If you know of any, please leave a comment below.

Going after the idea that excipients in the vaccine are what cause those with MTHFR variants (i.e. half the population) to be harmed by vaccines, I did find a very small study (50 participants) showing that those with the MTHFR C677T variant might be more sensitive to mercury.  But that really isn’t much of an issue since mercury has been removed from children’s vaccinations since 2001.  (Seasonal flu vaccines for those over 6 years old can still contain mercury.)

I didn’t find any other links between MTHFR variants and other excipients in vaccines.

In digging into the topic, I did find several studies looking at the interplay between genetics and vaccination reactions.  So there has been work done looking at genetic variants and the role they play in both the effectiveness of vaccines and in regards to adverse events, but those studies do not mention MTHFR as being involved in vaccine events.

One study found quite a few HLA gene variants as well as other immune system gene variants that do play a role in how vaccines work.  The study sums up: “We predict, based on the type of work discussed herein, a time when it will be possible to determine what diseases an individual is at risk for, what vaccine(s) they should receive, at what doses and the chance that they may experience any significant adverse event. This is a very different experience than the current situation where essentially everyone gets every vaccine, given in the same manner, at the same dose and the same number of doses – ignoring the reality that we are genetically preprogrammed to immunologically respond in predetermined differing patterns.”

To sum it up:

There is not a lot of evidence pointing to common MTHFR variants playing a role in vaccination adverse events.  There are other genetic variants that have been found to increase the risk of either adverse events or vaccine effectiveness.  I’ve listed some of the studies below.   Someday, hopefully, we will be at the point where those who are most susceptible to a disease will be able to get a vaccine that is genetically right for them.

More to read:



Bronwyn Davey · January 14, 2018 at 1:09 am

Thank you very much for this article, it has answered a lot of my questions. I too am interested in the science to prove what appears to be a connection.

    Paige · March 16, 2018 at 8:26 pm

    I was also looking for evidence and could not find any scientific studies either. It seemed odd to me. Then I find myself questioning why there are none? I would like to become educated more on this topic because I believe there is so much yet to be discovered.

      Debbie Moon · March 17, 2018 at 11:48 am

      I still find it strange that something that is so vehemently ‘known’ on Facebook groups and forums has no basis in scientific studies. The only information that I find is from Ben Lynch’s videos. It is his theory, not based on any study other than the one older study on smallpox vaccines.
      It does make sense that MTHFR C677T and A1298C wouldn’t play a big role in vaccine injury though, because the variants are too common – covering more than half the population.
      So my big question is still to wonder why there aren’t more studies tying other, probably much less common genetic variants to vaccine injury. We know vaccine injury happens, so why isn’t there a push to predict who is at risk?

        Katie Hartsfield · December 6, 2018 at 10:53 pm

        Some food for thought: Could we consider that 1 in 36 children are now being diagnosed with Autism. They qualifies as an epidemic…and would account for the 50% of the population discussed (actually more) above. Consider reading the book “How To End The Autism Epidemic” which covers this. A great, thought-provoking read with studies included. As an autism mom, it has taught me so much!

JLD · April 7, 2018 at 7:22 pm

I have MTHFR C677T mutation and prior to knowing this started noticing that right after getting my annual flu shot I would become seriously depressed and emotionally detached. It was like I could feel nothing. It would be really bad for weeks but linger for months. I took a DNA test and ran the raw data through some programs and thats when I found out about the mutation. I also have ADHD and have been B12 anemic off and on I asked my psych if there could be a tie between the flu shot, the depression and the gene mutation. He laughed it off. I haven’t had the shot in 2 years and haven’t had the same issues. I wish I could find a doctor that would take the tests seriously and help me find solitions. I have been eating more whole foods and taking 5- MTHF and B-12 methylcobalamin which seems to help. I have less anxiety, am more focused and more energy.

    Debbie Moon · April 9, 2018 at 5:08 pm

    It sounds like you are on the right track with getting more whole foods, folate and B12. I honestly don’t know how much the MTHFR variant plays a role in your reaction to the flu shot. There are probably quite a few different genes that are involved in your immune response to the vaccine and the additives in the vaccine. One thing to consider may be the timing of when you get the vaccine if it is in the fall/winter — could you be reacting to the change in seasons (SAD)? or could that be compounding the immune response that your body has to the vaccine? Whatever the reason, I’m glad that you are finding the solutions you need.

Angela sanchez · September 29, 2018 at 7:29 am

I came across this article while looking
Into vaccine injury as my questions are purely on a hunch. I have 3 children, two of which are MTHFRC-677T and one who is not. Both of the MTHFR children were immunized just like the other child but the MTHFR children both started showing signs of autism around 2 years old. I find it odd that one of the MTHFR children and one without are twins; one is autistic and the other is not. Any thoughts about this? Is it a coincidence or not?

    Debbie Moon · October 1, 2018 at 2:54 pm

    Hi Angela,
    I haven’t found any research that links MTHFR and vaccines to autism.
    The question of whether the child’s MTHFR variant adds to the risk of autism has been looked at in several different studies, but the results don’t always agree. There was a recent Chinese study that showed no increased risk of autism with the MTHFR C677T variant ( but other studies did show it increasing the risk a little bit ( This may be due to different diets in the populations studied.

    What you may want to look at instead is the research on folate levels and the mother’s MTHFR status — and how that all interacts with the baby’s genetics. My guess (keeping in mind that I’m not an autism expert nor a doctor) is that autism is multifactoral – prenatal environment, baby’s genetic susceptibility, mother’s genetics, epigenetics, and the gut microbiome.

    Here are a couple of studies that you might find interesting: — this has a good section on how the microbiome (folate and B12 production from gut microbes) interacts with the methylation cycle as well as with MTHFR variants.

    Are you familiar with Dr. Amy Yasko’s work with the methylation cycle and autism?

    Best of luck to you as you continue your search for answers on this. Let me know if you need help with finding other research on the topic — I’m sure your online time is limited with three kids, two with autism and twins to boot!

Lauren · December 3, 2018 at 10:32 pm

According to this study there is still minute amounts of mercury in one infant vaccine. Infanrix hexa.

    Debbie Moon · December 4, 2018 at 12:03 am

    Hi Lauren,
    Thanks for commenting and adding that study. Looks like that is a vaccine that is still in use in Australia, UK, NZ, and possibly Canada.

    Debbie Moon · December 31, 2018 at 12:26 pm

    Thanks for adding these.
    Looks like both are reviews of studies on adverse events from vaccinations. The information on the MTHFR variant in both reviews is just referring back to that one single small study of the smallpox vaccine.
    Thanks for reading and commenting.

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