Does the HPV Vaccine Increase Risk of Blood Clots?

Check out this answer from Consensus:

Both studies reviewed provide strong evidence that the HPV4 vaccine does not increase the risk of venous thromboembolism among females aged 9-26 years. These findings should reassure healthcare providers and patients about the safety of the HPV4 vaccine in terms of blood clot risk.

The quadrivalent human papillomavirus vaccine (HPV4) has been widely administered since its approval by the Food and Drug Administration (FDA) in 2006. Despite its benefits in preventing HPV-related diseases, concerns have been raised about a potential association between HPV4 and venous thromboembolism (VTE). This article reviews the findings from two significant studies to determine whether the HPV vaccine increases the risk of blood clots.

Study 1: Evaluation of VTE Risk Post-HPV4 Vaccination

Objective

The first study aimed to evaluate the risk of VTE among females aged 9-26 years who received the HPV4 vaccine between 2006 and 20131.

Methods

Researchers utilized a self-controlled risk interval design, comparing the incidence of first-ever VTE in risk intervals (Days 1-28 and Days 1-7 post-vaccination) to control intervals (Days 36-56 for Dose 1 and Days 36-63 for Doses 2 and 3). The study accounted for potential confounding factors, such as combined hormonal contraceptive use.

Results

Out of 279 potential VTE cases identified following 1,423,399 HPV4 doses, 53 were confirmed as first-ever VTE. Importantly, all confirmed cases had known risk factors for VTE. The study found no elevated risk of VTE in the first 7 or 28 days following any dose of HPV4. The relative risk estimate for the 28-day risk interval was 0.7 (95% CI: 0.3-1.4), indicating no significant increase in VTE risk1.

Conclusion

The study concluded that there is no evidence of an increased risk of VTE associated with HPV4 among females aged 9-26 years. The robust control for both time-invariant and contraceptive-related time-varying potential confounding factors strengthens this conclusion1.

Study 2: Absence of VTE Risk Following HPV4 Vaccination

Objective

The second study investigated the potential association between HPV4 vaccination and VTE in adolescents and young adults aged 9-26 years from 2008 to 20112.

Methods

This self-controlled case series study identified potential VTE cases diagnosed within the study period who had received at least one dose of HPV4. Confirmed cases were reviewed, and incidence rate ratios (IRRs) were calculated to estimate VTE risk in the 1-60 day period following HPV4 exposure, with stratification by age, gender, hormonal contraceptive use, and recent surgery or trauma.

Results

Out of 313 potential VTE cases, 156 were confirmed. Nearly all confirmed cases had at least one known risk factor for VTE. The risk of VTE varied, with an IRR of 1.47 (95% CI: 0.47-4.64) in the 1-7 days following HPV4 exposure and 0.92 (95% CI: 0.54-1.57) in the 1-60 days following vaccination. The study found no significant increase in VTE risk post-HPV4 exposure2.

Conclusion

The study concluded that the risk of developing VTE among 9- to 26-year-olds was not elevated following HPV4 exposure. The limited sample size restricted the ability to evaluate potential effect modifiers rigorously, but the overall findings support the safety of the HPV4 vaccine concerning VTE risk2.

Does the HPV vaccine increase risk of blood clots?

Ian Frazer has answered Unlikely

An expert from University of Queensland in Vaccines, Vaccinology

There is no data suggesting and increased incidence of blood clots following HPV vaccine when compared with unvaccinated individuals in the VAERS registry, and no a priori reason why this and other similar vaccines (alum adjuvant and protein) should promote blood clots.