Another massive study supports safety of the HPV vaccine

gardasil-1-lessA study published in BMJ (British Medical Journal) reaffirms the overall safety to teenage girls of the HPV quadrivalent vaccine, also known as Gardasil (or Silgard in Europe). The vaccine prevents infection by human papillomavirus, a sexually transmitted disease, specifically subtypes 16 and 18, that cause not only approximately 70% of cervical cancers, but also they cause most HPV-induced anal (95% linked to HPV), vulvar (50% linked), vaginal (65% linked), oropharyngeal (60% linked) and penile (35% linked) cancers.

The viruses are generally passed through genital contact, almost always as a result of vaginal, oral and anal sex. There is strong clinical evidence that the incidence of HPV infections have declined since the launch of the HPV vaccine and the subsequent steady rate of HPV vaccination.

This BMJ study also supports another large study published in 2012, which included nearly 200,000 young females who had received the vaccine, and found that the vaccine was only associated  with same-day syncope (fainting) and skin infections in the two weeks after vaccination.

The size of this was impressive. The authors reviewed the records of 997,585 Danish and Swedish girls, aged 10-17, to determine their HPV vaccination status. They determined that 296,826 of those girls received the quadrivalent HPV vaccine, a total of 696,420 doses of the vaccine. Look at that carefully, 696 thousand doses. That number is so high, that even minor adverse events may be uncovered. Except, unsurprisingly, none were found.

The researchers examined patient records for 53 different diagnoses requiring hospital or specialist care, including blood clots, neurological diseases, and autoimmune diseases such as type 1 diabetes between immunized and non-immunized groups. The limited the study to 180 days post-immunization (except for thromboembolic events, which they limited to 90 days). Out of the 53 adverse events, 24 were eliminated from the study because <5 events were observed in the vaccinated group (which would become statistically impossible to analyze).

Of the remaining 29 adverse events, the results are shown in the table below.

Rates of adverse events according to quadrivalent human papillomavirus (qHPV) vaccination status, cohort of adolescent girls aged 10-17 years in Denmark and Sweden, October 2006-December 2010
Rates of adverse events according to quadrivalent human papillomavirus (qHPV) vaccination status, cohort of adolescent girls
aged 10-17 years in Denmark and Sweden, October 2006-December 2010

Out of these 29 events, 26, including all of the neurological incidents, showed no statistical difference in risk between the vaccinated and unvaccinated group. Three, Behcet’s syndrome, Raynaud’s disease, and type 1 diabetes (all autoimmune associated diseases) showed small, but statistically significant higher risks in vaccinated individuals. However, because of several factors, including random response time post-vaccination and the fact that the incidence rate for the three mirrored what is found in the general population of girls of this age, the authors determined that their was no evidence of a causal relationship.

According to the authors,

Although significantly increased rate ratios were initially observed for three outcomes, further assessment showed no consistent evidence for a plausible association; firstly, these risk signals were relatively weak, as assessed by prespecified criteria, and, secondly, no temporal relation between vaccine exposure and outcome was evident.

The authors then concluded that,

this study identified no safety signals with respect to autoimmune, neurological, and venous thromboembolic events after the qHPV vaccine had been administered.

The lead author of this study, Dr. Lisen Arnheim-Dahlström, associate professor at Karolinska Institutet’s Department of Medical Epidemiology and Biostatistics stated, “you could see our study as part of a societal alarm system, and as such it did not alert us to any signs that HPV vaccination carries a risk of serious adverse events. We will, of course, be continuing to monitoring HPV vaccination in terms of both this and its efficacy over time.”

Note: this study was supported by a grant from the Swedish Foundation for Strategic Research and the Danish Medical Research Council. The funding bodies had no role in the study design; the collection, analysis, and interpretation of the data; the writing of the article; and the decision to submit it for publication. All authors are independent from the funding agencies.

Once again, we have evidence, in the form of a impressively large retrospective epidemiological analysis, that none of these serious adverse events were more common in the vaccinated group than in the unvaccinated group. None.

Let’s review: Gardasil no serious risks. Gardasil prevents cancer. It’s a no brainer.


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