Researchers at Karolinska Institutet in Sweden and their Danish colleagues have monitored HPV-vaccinated girls via patient data registries in order to examine the incidence of a wide range of diseases and thus determine if there are any serious adverse effects of the vaccine. Their results show no significant increase of the examined diseases in the vaccinated girls relative to their unvaccinated peers.
The study included almost a million Swedish and Danish girls born between 1988 and 2000, and compared roughly 300,000 girls who had been HPV vaccinated with 700,000 who had not. All the girls were between 10 and 17 at time of vaccination, and the vaccines had been administered at some time between 2006 and 2010. The researchers then used patient registries in Denmark and Sweden to study the incidence of any serious adverse effects of the vaccine.
The researchers examined 53 different diagnoses requiring hospital or specialist care, including blood clots, neurological diseases, and autoimmune diseases such as type 1 diabetes. They found that none of these diseases were more common in the vaccinated group than in the unvaccinated group. Mild adverse effects, such as temporary fever and swelling at the site of injection, were not studied however.
"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," says Dr Lisen Arnheim-Dahlström, associate professor at Karolinska Institutet's Department of Medical Epidemiology and Biostatistics. "We will, of course, be continuing to monitoring HPV vaccination in terms of both this and its efficacy over time."
In Sweden, HPV vaccination has been available through the general vaccination programme to girls between the ages of 11 and 12 since 2012. Over 120 million doses of the HPV vaccine used in Sweden (Gardasil) have been administered around the world. The majority of adverse effects reported to the Swedish Medical Products Agency have included fever, headache, local swelling at the site of injection and other mild reactions. However, as the present study did not consider data from primary care, such mild events do not appear in its results.
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"Autoimmune, neurologic, and venous thromboembolic adverse events following administration of a quadrivalent HPV-vaccine to adolescent girls: a cohort study in Denmark and Sweden", Lisen Arnheim-Dahlström, Björn Pasternak, Henrik Svanström, Pär Sparén and Anders Hviid, British Medical Journal, online 9 October 2013.