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HPV vaccination not linked to VTE
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Quadrivalent HPV vaccination was not associated with increased risk for venous thromboembolism, according to results of a self-controlled case-series study.
Two postlicensure safety studies suggested a potential association between HPV vaccination and subsequent venous thromboembolism (VTE). An analysis of data from the Vaccine Adverse Event Reporting System showed high rates of VTE incidence after HPV vaccination, and data from the Vaccine Safety Datalink demonstrated a twofold risk for VTE in this patient population, according to background information provided by researchers.
“[However], one was based on reports from a passive surveillance system and the other included few vaccinated cases, many with known risk factors for VTE,” Nikolai Madrid Scheller, MB, of the department of epidemiology research at Statens Serum Institut in Copenhagen, Denmark, and colleagues wrote.
In the current study, Scheller and colleagues assessed VTE incidence in more than 1.6 million Danish females aged 10 to 44 years. About one-third of the study population (n=500,345; 31%) received the quadrivalent HPV vaccination between 2006 and 2013.
Researchers reported 4,375 cases of VTE in the study population; of these, 889 (20%) occurred after HPV vaccination.
Scheller and colleagues evaluated the incidence of VTE within the primary risk period, defined as within 42 days of HPV vaccination. They compared that rate with VTE incidence during the control period, which included incidence in unvaccinated women and VTE cases that occurred in vaccinated women after the 42-day primary risk period elapsed.
The researchers calculated crude incidence rates of 0.126 events per person-year in the primary risk period and 0.159 events per person-year during the control period (incidence ratio, 0.77; 95% CI, 0.53-1.11). Researchers observed a similar trend after controlling for contraceptive use (incidence ratio, 0.8; 95% CI, 0.55-1.16).
HPV vaccination was not associated with increased VTE risk in women aged 10 to 24 years (incidence ratio, 0.66; 95% CI, 0.4-1.09) or in women aged 25 to 44 years (incidence ratio, 1; 95% CI, 0.56-1.8).
Among those who received the vaccination, crude incidence rates increased over time. Researchers reported 0.102 events per person-year within 14 days of vaccination (adjusted incidence ratio, 0.77; 95% CI, 0.53-1.11). The rate increased slightly to .103 events per person-year in the period of 15 to 28 days post-vaccination (adjusted incidence ratio, 0.62; 95% CI, 0.31-1.27). The rate peaked at .174 events per person-year in the period from 29 to 42 days post-vaccination (adjusted incidence ratio, 1.06; 95% CI, 0.61-1.83).
“Our results … do not provide support for an increased risk of VTE following quadrivalent HPV vaccination,” Scheller and colleagues wrote.
Disclosure: The researchers report no relevant financial disclosures.
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