The quadrivalent human papillomavirus vaccine does not increase the risk of venous thromboembolism, a study showed.
Two previous studies finding an association, one based on the Vaccine Adverse Event Reporting System and the other on the Vaccine Safety Datalink, reported few vaccinated cases, many of whom had known venous thromboembolism (VTE) risk factors, Nikolai Madrid Scheller and his colleagues at Statens Serum Institut in Copenhagen reported in a research letter (JAMA 2014;312:187-8).
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HPV vaccines do not increase VTE risk, said Dr. Scheller and his colleagues.
The team used the self-controlled case series method with the main risk period for a first diagnosis of VTE set at 1-42 days after vaccination. They excluded women who were likely pregnant at the time of the VTE or had undergone major surgery in the previous 4 weeks or had a cancer diagnosis in the previous year from the VTE.
Women with VTE aged 10-44 years were followed until the end of the study or until emigration, death, or age 45 years during the study period from Oct. 1, 2006, to July 31, 2013. Among the 1.6 million women in the population cohort, 31% had received the quadrivalent HPV vaccine, and 4,375 women had VTE, 20% of whom had been vaccinated and served as the self-controlled cases.
The researchers found no association between the quadrivalent HPV vaccine and VTE (incidence ratio, 0.77). The lack of association remained in subsequent analyses adjusting for age and oral contraceptive use, and using only cases of VTE in which the women were receiving anticoagulants 4 weeks after diagnosis.
The study did not report external funding. The authors reported no disclosures.