Health and Science News for Parents

HPV vaccine and multiple sclerosis: Reassuring findings about Gardasil safety

written by Tara Haelle

I wrote yesterday about the MMR and varicella vaccines and noted that I frequently hear concerns about the MMR. In recent years, however, parents’ concerns about HPV seem to have eclipsed those about the MMR. Gardasil and Cervarix are newer vaccines, and they are given in older girls and boys to protect against a virus that is most commonly (but not exclusively) transmitted through sexual contact, so there are probably all sorts of cultural hesitations tied up in the usual safety concerns that people have about vaccines when it comes to this particular one.

Still, the HPV vaccine is the only one we have that was developed *specifically* to prevent cancer (though two strains in Gardasil also prevent genital warts). The hepatitis A and B vaccines also indirectly prevent a proportion of liver cancer cases since liver cancer can develop from hepatitis. But every single cervical cancer case is caused by one HPV strain or another, so preventing HPV means preventing cervical cancer directly. Further, HPV can cause penile, anal and head and neck cancers, which are rarer than cervical cancer – and can develop due to other causes – but are killers nonetheless that the HPV vaccine can partly prevent (and quite effectively).

MS can significantly impede physical activities, but this study didn't find any link between MS and the HPV vaccine. Photo by Joshua Davis.

MS can significantly impede physical activities, but this study didn’t find any link between MS and the HPV vaccine. Photo by Joshua Davis.

But ah… safety concerns. In the not-so-distant future, I have a project planned to look at every HPV concern and misconception out there, but for now, I’m just focused on a new study in JAMA that looked at multiple sclerosis and other demyelinating diseases. I wrote about this study in depth over at Forbes, so I encourage you to read that piece for the raw numbers and specifics on risk, but I’m adding a few things here.

First, what’s a demyelinating disease? It’s any condition in which myelin, the protective sheath around nerves, starts degrading, which means electrical messages can’t travel from one nerve cell to the next as quickly as they should. Multiple sclerosis is the best known of these, but it’s not the only one. Others include optic neuritis, neuromyelitis optica, transverse myelitis and acute disseminated encephalomyelitis, among others.

A handful of case studies have reported on multiple sclerosis or another demyelinating disease starting after HPV vaccination, such as one describing five patients whose symptoms began within three weeks of vaccination. These are the sorts of case studies that anti-vaccine advocates cherry-pick in promoting fear and misinformation about vaccines. Such studies are actually very important to investigating vaccine safety because they alert the medical community to a condition that occurred around the same time as a vaccination and *might* be related – but it’s important to remember that they can’t actually show that there was a link at all. These reports aren’t canaries in the coal mine. Rather, they’re calling attention to something worth studying further. They’re a way to say, “Hey, here’s something interesting. Come check this out. Maybe we ought to look for this in other people too!” And then other researchers come along and design extremely large safety studies to see if there could be a link between the vaccine and that condition.

When looking for these conditions, the rarer they are, the larger a sample size you need in a study. Otherwise, researchers can’t detect enough cases to compare among vaccination and unvaccinated individuals and to compare to background rate – the usual rate of that disease in a population (the prevalence). So, having thousands of people to study is helpful. Even better is a sample that comprises an entire nation’s population, and that’s exactly what this study did.

The researchers included every Swedish and Danish female from age 10 to age 44 who didn’t have MS or another demyelinating disease during the time period from October 2006 (a month after Gardasil was licensed in Europe) to December 2012 (for the Swedish residents) and July 2013 (for the Danish residents). Because Denmark and Sweden both have nationalized health care systems, researchers can access the medical records for all Danish and Swedish citizens, providing complete health histories without bias for everyone in the country.

What’s cool about this study is that they conducted two separate statistical analyses: first comparing vaccinated individuals to unvaccinated individuals and then comparing vaccinated individuals to themselves – their risk in the two years after vaccination versus their risk after those two years or before vaccination. That’s called a self-controlled case series design, my favorite study design because it so cleverly removes any possible confounding variables, or differences, between individuals since each person is compared to themselves. (You don’t have to control for income, age, sex, health behaviors, sexual history, drug history, geography or any number other factors because you’re not even comparing different people.) The researchers chose two years for the window of possible risk because a U.S. study showed it takes less than a year for more than half of all MS cases to be diagnosed.

And what did they find? Again, you can read the specifics on the numbers over at Forbes, but basically, they didn’t find a link at all. There was no evidence to suggest that the HPV vaccine was associated with multiple sclerosis or the other demyelinating diseases. (The authors even tweaked their findings with additional statistical analyses to see if they could basically do anything to make an increased risk of those diseases show up, but nope, they couldn’t. There just isn’t a link. Nada.)

So, that’s encouraging, but every study – even a massive, well-conducted, multiple-analysis one like this one – has weaknesses. In this one, even though researchers had a huge population to work with here – literally all the girls and women in the right age group from two Scandinavian countries – these diseases are rare enough that the authors still have limitations in what they can detect. If the increased risk of multiple sclerosis with a vaccine were less than three times greater (if, for example, the HPV vaccine doubled the risk but didn’t triple it), this study couldn’t necessarily rule that out as a possibility. Likewise, if a risk of any other demyelinating disease were less than double (if it increased the risk 30% but not 100%, or double), that couldn’t be ruled out either. In practical terms, that means if there were any increased risk, it’s very low and it’s rare, but taken with all the other studies that have also not found a link, it really means that, again, we have no evidence at all connecting the HPV vaccine to multiple sclerosis or any other demyelinating disease.


Note: The study was funded by the Swedish Foundation for Strategic Research, Novo Nordisk Foundation and the Danish Medical Research Council.

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4 Responses to “HPV vaccine and multiple sclerosis: Reassuring findings about Gardasil safety”

  1. Thanks so much for breaking down the science. There’s a lot of superstition around vaccinations!

  2. People who have never gone through the horrors of childhood diseases such as measles, diptheria, whooping cough & the like tend to be skeptical about the value of vaccines. My grandmother lost two infants to whooping cough and one to diptheria. The next scourge was polio. My four children had all the vaccines available. Our doctor had been to medical school & knew more than I did & I knew the danger of the diseases.

  3. Melanie Dailey

    My son did in fact have a demyelinating lesion approximately 2-3 weeks after 2nd dose of HPV. I do believe there is a connection even if it’s that my son is the one in a million for something like this to happen to.

    • Tara Haelle

      I cannot prove or disprove the association. All we can say is that no evidence has found such a link.

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