Anti-vaccine activists tend to grab onto any story that supports their narratives about vaccines. Generally, they comb the internet for any article that either tells us that vaccines don’t work, that they’re dangerous, or that the disease prevented is innocuous. It’s a frustrating process. Recently, an article was published that seemed to indicate chickenpox prevents glioma, a rare group of cancers that arise in the brain or spine. Then, by extension, some have claimed that not being vaccinated against chickenpox helps prevent glioma.
But is this valid? What does the evidence say about chickenpox and glioma? Is it even plausible that chickenpox has some biological relationship to glioma?
As always, answers aren’t as simple as the anti-vaccine group would like them to be. It’s complicated, as most science is.
What is glioma?
Gliomas are a group of 10 cancers that arise in glial cells of the brain or spine. Gliomas make up about 30% of all brain and central nervous system tumors, along with 80% of all malignant brain tumors.
The prognosis for someone with a high-grade glioma is poor. In the USA, depending on the type of glioma diagnosed, the five year survival rate ranges from >94% for pilocytic astrocytoma down to <5% for glioblastoma.
Gliomas are rarely curable. The treatment regimen is a combination of surgery, radiation therapy, and chemotherapy, but even then, the prognosis is still poor for most types of gliomas. And since this is a thing on the internet, hash oil does not “cure” gliomas.
The overall incidence of gliomas in the USA is around 4.0-5.0 per 100,000 individuals, or about 0.004-0.005% irrespective of other risk factors. In other words, gliomas are very rare cancers indeed. One last thing, save this information for later in the article, because it’s an important point.
What about the chickenpox prevents glioma narrative?
In an article recently published in Cancer Medicine, Amirian et al. examined data from the Glioma International Case-Control Study (GICC), an international consortium with 14 recruitment sites across the world. Cases were defined as individuals within 18–80 years of age (at diagnosis) who had one of 10 different glioma types. Data was collected using a written questionnaire, with follow-up, from all 14 recruitment sites.
The researchers evaluated 4,533 cases and 4,171 controls from all recruitment locations. The most important result, the one on which we will focus, is that 79% of the glioma cases and 83% of controls reported a positive history of chickenpox. A positive history of chickenpox was associated with a 21% lower glioma risk, only controlling for age and sex. The history of chickenpox in this group is relatively high because the chickenpox (varicella zoster virus or VZV) vaccine has only been available since 1995 in the USA. Thus, of the age group 18-80, most were at risk of chickenpox before the vaccine was made widely available and recommended for children.
If you take this study at face value, you might think to yourself that vaccinating against varicella is a bad idea, because it could prevent glioma. But is that wise?
We need to take a more critical look at this data. Here are my concerns:
- The study only adjusted for age and sex confounders (that is, variables that may account for the difference). I can imagine other confounding data that should have been examined to see if it gives other interpretations of the data, like diet, smoking, and other known cancer risk factors. In fact, did the researchers examine other risk factors that might have shown some relationship between it and gliomas?
- The study relied upon written questionnaires. Johansen et al. strongly criticized GICC’s methodology by stating, “we recommend that the questionnaire-based case-control design be placed lower in the hierarchy of studies for establishing cause-and-effect for diseases such as glioma. We suggest that a state-of-the-art case-control study should, as a minimum, be accompanied by extensive validation of the exposure assessment methods and the representativeness of the study sample with regard to the exposures of interest. Otherwise, such studies cannot be regarded as ‘hypothesis testing’ but only ‘hypothesis generating’.” In other words, the study from Amirian et al. helps us establish a hypothesis, chickenpox reduces the risk of gliomas, but it does not actually test the hypothesis.
- There is a lack of plausibility offered for this hypothesis. One could posit that since VZV hides in the nervous system after a chickenpox infection – sometimes reactivating and coming back as shingles – it somehow blocks the mutation of glial cells that causes the formation of gliomas. However, glial cells have a different function than neuronal cells, which can generally harbor the varicella virus. As far as I know, the varicella virus does not hide out in glial cells, which would negate a plausible relationship.
- It is more plausible that the antibodies against VZV have some unknown effect on the formation of gliomas. And if this were the case, then the chickenpox vaccine, which induces the formation of antibodies against the varicella virus, could have the same effect on gliomas as a chickenpox infection. And that’s a major problem with this glioma study – the study population did not include many individuals who were vaccinated (and it wasn’t clear how many were). If one is going to make a very risky claim, that contracting chickenpox can prevent glioma, then you better provide us with data that shows whether vaccinated individuals have or don’t have the same protection.
But there is one more thing that troubles me about the narrative pushed here – what are the relative risks of contracting gliomas (admittedly, a very dangerous group of cancers) vs. the risk of serious complications from chickenpox, if one believes that chickenpox has some protective effect.
As many of us have seen, there are beliefs that chickenpox is a minor disease, unworthy of being compared to something like glioma. Except that belief is completely untrue. Let’s take a look at some of the complications of chickenpox:
- About 20% of patients who contract chickenpox develop shingles later in life. Shingles is a painful and damaging reoccurrence of the original chickenpox infection (usually decades later).
- Pregnant women are at high risk of damage to the fetus from chickenpox.
- The risk of serious complications of chickenpox, including hospitalization and death, is approximately 260 per 100,000. That’s over 50X higher than the risk of gliomas, which, as I wrote above, is around 4.0-5.0 per 100,000 people.
To be fair, Amirian et al. did not conclude their paper by claiming anything along the lines of “end chickenpox vaccines because we need to protect ourselves from glioma.” In fact, the authors left the door wide open that it’s possible that the immune response to chickenpox or the VZV vaccine may protect against gliomas. Given the quality of this study, and an incomplete examination of all risk factors, including comparing vaccinated and unvaccinated populations, one cannot make any responsible conclusion about gliomas and chickenpox.
The TL;DR version
If I were making a recommendation based on the study of chickenpox and gliomas, I’d say that the risk from chickenpox far exceeds the risk of getting glioma. In other words, get the chickenpox vaccine because we know the risk of the infection, we know the risk of gliomas, and we don’t have any solid evidence that contracting chickenpox or getting the vaccine has any measurable effect on glioma risk.
To make a leap from an untested hypothesis, that chickenpox prevents glioma, to not vaccinating your children is probably not the logical or responsible choice.
- Amirian ES, Scheurer ME, Zhou R, Wrensch MR, Armstrong GN, Lachance D, Olson SH, Lau CC, Claus EB, Barnholtz-Sloan JS, Il’yasova D, Schildkraut J, Ali-Osman F, Sadetzki S, Jenkins RB, Bernstein JL, Merrell RT, Davis FG, Lai R, Shete S, Amos CI, Melin BS, Bondy ML. History of chickenpox in glioma risk: a report from the glioma international case-control study (GICC). Cancer Med. 2016 Jun;5(6):1352-8. doi: 10.1002/cam4.682. PubMed PMID: 26972449; PubMed Central PMCID: PMC4924393.
- Goodenberger ML, Jenkins RB. Genetics of adult glioma. Cancer Genet. 2012 Dec;205(12):613-21. doi: 10.1016/j.cancergen.2012.10.009. Review. PubMed PMID: 23238284.
- Johansen C, Schüz J, Andreasen AS, Dalton SO. Study designs may influence results: the problems with questionnaire-based case-control studies on the epidemiology of glioma. Br J Cancer. 2017 Mar 7. doi: 10.1038/bjc.2017.46. [Epub ahead of print] PubMed PMID: 28267708.
- Ostrom QT, Bauchet L, Davis FG, Deltour I, Fisher JL, Langer CE, Pekmezci M, Schwartzbaum JA, Turner MC, Walsh KM, Wrensch MR, Barnholtz-Sloan JS. The epidemiology of glioma in adults: a “state of the science” review. Neuro Oncol. 2014 Jul;16(7):896-913. Review. PubMed PMID: 24842956; PubMed Central PMCID: PMC4057143.
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