HPV vaccination and risk of MS

As long as the cause of multiple sclerosis (MS) remains unknown, it will be tempting – for patients and doctors alike – to search for an explanation among events that occurred before the diagnosis. This approach, known from antiquity as post hoc, ergo propter hoc (after the fact, therefore because of the fact), though sometimes successful, can also be misleading. History of science in general, and multiple sclerosis in particular, is rife with such fallacies. It is important to remember then, that this approach is best thought of as “brainstorming”, generating potential leads, but (almost) never the definitive proof. 

Human papillomavirus (HPV) is a virus associated with uterine cancer. Since 2006, vaccination against HPV has been available. As with many other vaccines, sporadic reports associating HPV vaccine with new onset MS surfaced soon thereafter. To properly evaluate such claims, however, one would have to compare entire populations of vaccine recipients versus non-recipients over long periods of time. This has now been accomplished through the use of national health registries of Denmark and Sweden (such work is much harder to do in the United States, as our health care is so fractionated that long-term follow-up is all but impossible).

In a cohort of almost four million females aged 10 to 44, followed from 2006 to 2013, approximately 800,000 women received the vaccine. Vaccine recipients’ risk of developing MS was the same as that of unvaccinated women in the two years following the vaccination. The same was found to be the case with regard to other demyelinating diseases (optic neuritis or transverse myelitis), which sometimes predict MS. In the words of the authors: "These findings do not support concerns about a causal relationship between HPV vaccination and demyelinating diseases.”

Will this be a final nail in the coffin of this theory? Probably not for everyone. My former mentor once said that when a strongly held belief collides with the fact, the belief always wins. For the rest, however, the facts will suffice.