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No Evidence of Murine Leukemia Virus-Related Viruses in Live Attenuated Human Vaccines

Posted Jan 04 2012 9:39pm

There has been much discussion of XMRV, Xenotropic murine leukemia virus-related virus , here at Left Brain/Right Brain and elsewhere in the past few months. The reason for the discussion here is the (now shown to be false) idea that XMRV is implicated in autism causation. Two papers have addressed this question and found no evidence of a link. XMRV came to prominence as a possible candidate in causing chronic fatigue syndrome (CFS). Multiple papers have found no evidence of a link between XMRV and CFS (f an example is discussed here ) and the original paper on the topic was withdrawn by editors of the journal Science after it became clear that those results were suspect.

The idea that autism and XMRV was promoted by David Kirby, whose efforts also strongly promoted the debunked autism-epidemic-caused-by-mercury idea. Mr. Kirby’s article at the Huffington Post was . In this he quoted CFS/XMRV researcher Judy Mikovits:

And then Dr. Mikovits dropped a bombshell that is sure to spark controversy.

“On that note, if I might speculate a little bit,” she said, “This might even explain why vaccines would lead to autism in some children, because these viruses live and divide and grow in lymphocytes—the immune response cells, the B and the T cells. So when you give a vaccine, you send your B and T cells in your immune system into overdrive. That’s its job. Well, if you are harboring one virus, and you replicate it a whole bunch, you’ve now broken the balance between the immune response and the virus. So you have had the underlying virus, and then amplified it with that vaccine, and then set off the disease, such that your immune system could no longer control other infections, and created an immune deficiency.”

Mr. Kirby went on to write:

So there you have it – a possible explanation of regressive autism in a significant number of cases associated with immune system deregulation triggered by vaccination.

Of course, much more work is needed to nail down the exact significance of such an association. For example, is the virus implicated in the cause of autism, or do children harbor the virus as a result of autism?

Yes, Ms. Mikovits and David Kirby were proposing a possible link between autism, XMRV and (of course) vaccines.

That was October 2009. Fast forward to today, two years later and we see

A) Neither Ms. Mikovits nor anyone else has published the data supposedly linking XMRV and autism

B) Two studies have looked for evidence (and failed to find any) of a link between XMRV and autism,



C) Evidence has arisen that much of the data linking XMRV to CFS is faulty.

Studies on XMRV are still ongoing. If experience from the vaccine-autism-epidemic idea tell us anything, the idea that XMRV causes CFS and/or autism will die slowly and even more data are needed.

To that end, a recent study explored whether XMRV is a contaminant in live virus vaccines. (note that in other vaccines, the XMRV is likely as dead as the other constituents of the vaccine). You can tell the result from the title: No Evidence of Murine Leukemia Virus-Related Viruses in Live Attenuated Human Vaccines .


The association of xenotropic murine leukemia virus (MLV)-related virus (XMRV) in prostate cancer and chronic fatigue syndrome reported in previous studies remains controversial as these results have been questioned by recent data. Nonetheless, concerns have been raised regarding contamination of human vaccines as a possible source of introduction of XMRV and MLV into human populations. To address this possibility, we tested eight live attenuated human vaccines using generic PCR for XMRV and MLV sequences. Viral metagenomics using deep sequencing was also done to identify the possibility of other adventitious agents.


All eight live attenuated vaccines, including Japanese encephalitis virus (JEV) (SA-14-14-2), varicella (Varivax), measles, mumps, and rubella (MMR-II), measles (Attenuvax), rubella (Meruvax-II), rotavirus (Rotateq and Rotarix), and yellow fever virus were negative for XMRV and highly related MLV sequences. However, residual hamster DNA, but not RNA, containing novel endogenous gammaretrovirus sequences was detected in the JEV vaccine using PCR. Metagenomics analysis did not detect any adventitious viral sequences of public health concern. Intracisternal A particle sequences closest to those present in Syrian hamsters and not mice were also detected in the JEV SA-14-14-2 vaccine. Combined, these results are consistent with the production of the JEV vaccine in Syrian hamster cells.


We found no evidence of XMRV and MLV in eight live attenuated human vaccines further supporting the safety of these vaccines. Our findings suggest that vaccines are an unlikely source of XMRV and MLV exposure in humans and are consistent with the mounting evidence on the absence of these viruses in humans.

Yes, there is no evidence of XMRV in vaccines. This is rather anticlimactic given the evidence already in place that XMRV is not linked to autism, and the fact that the XMRV/CFS link is already tenuous at best.

The blogger erv has done the most thorough job following the XMRV study out there, including discussing the paper above . Others have taken up where David Kirby left off and promoted the idea that XMRV and autism are linked, and that vaccines are a possible part of that link. I would hope that those people would see the value in letting their readers know about this paper (and others, and the retractions).

  1. Neuroskeptic:
    So a virus that doesn't do anything, is not present in vaccines, which don't cause autism. Check mate.
  2. Jack:
    Great to see you covering this paper. I would like to think that Kirby will also cover this - he must have some idea of how hopes can be so easily and wrongly raised by mere speculation. He is therefore morally obliged at least to cover the retractions and this lack of association with vaccines. He knows the score.
  3. _Arthur:
    A throwaway hypothesis takes just minutes to be uttered on the web, and take years and hundred of thousands of dollars of research grants to scientifically disprove. Like, say, the throwaway hypothesis that "autistic children are bad mercury excretors". And no matter how soundly the -throwaway- hypothesis has been disproven, it will be used again and again and again by the denialists. They don't need research, they just need to feed their own inner certainties.
  4. Chris:
    If Kirby was moral he would have withdrawn is book Evidence of Harm. Especially after he predicted autism would decrease four years after thimerosal was removed from pediatric vaccines in 2002.
  5. Prometheus:
    As has been noted above, this study shows that a virus - XMRV - that hasn't been shown to cause disease in humans isn't present in vaccines. So, an off-the-cuff comment by a researcher results in the need to spend thousands of dollars and who knows how much research time to show that something that isn't a problem in humans also isn't present in vaccines. The terrible reality is that this study - no matter how good it is - will have absolutely no effect on those people who are now "convinced" that XMRV in vaccines causes autism, because they also believe that anyone who contradicts their beliefs - even if the have real data - is conspiring to hide the "True Cause of Autism". What a mess! Prometheus


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