HPV Shot Not Linked to Blood Clots

HPV vaccine not associated with venous thromboembolism in large population study

(RxWiki News) One of the few vaccines that can actually protect against cancer is the human papillomavirus (HPV) vaccine, which prevents four strains of HPV. But some parents have expressed concerns about the safety of the HPV vaccine.

A recent study found that blood clots were not a concern for women who received the HPV vaccine.

HPV is a sexually transmitted disease that can cause cervical cancer as well as throat and neck cancers and penile and anal cancers.

The "quadrivalent" HPV vaccine, Gardasil, protects against the four strains of HPV most associated with causing cancer.

"Discuss vaccinations with your daughter's pediatrician."

This study, led by Nikolai Madrid Scheller, MB, of the Department of Epidemiology Research at Statens Serum Institut in Denmark, looked at whether there was an increased risk of venous thromboembolism with the HPV vaccine.

A "venous thromboembolism" is a blood clot in the veins that breaks free and travels through the body toward the lungs, where it could be fatal.

The researchers investigated the records of all Danish women aged 10 through 44 from October 2006 through July 2013, which included more than 1.6 million women.

About a third of the women overall (31 percent, or about half a million) had received the HPV shot, and 4,375 women had experienced a blood clot.

Twenty percent of the women who had experienced a blood clot had also received the HPV vaccine, so these were the women the researchers focused on.

The researchers excluded all the women who had been pregnant when they had the blood clot because blood clots are more common during pregnancy. They also excluded women who had had a cancer diagnosis in the year before the clot or major surgery in the four weeks before the clot since these are also risk factors.

Then the researchers looked at when the women had experienced the blood clot and whether it was within the 42 days after being vaccinated. They compared the timing of the blood clots among the women to see if more incidents were occurring after the vaccination rather than before or much later.

The results showed that here was no association between the quadrivalent HPV vaccine and venous thromboembolism during the 42 days following vaccination.

In fact, they were a little less likely to experience a blood clot in the 42 days after the vaccine than during a time period before the shot or after the 42-day "risk window."

This finding was before they made any adjustments for other risk factors related to blood clots.

When the researchers made adjustments for women's age and use of birth control pills, there was still no association between blood clots and the HPV shot.

The same was true when the researchers looked only at the women taking blood thinners a month after their clot, which confirms that they had a serious blood clot at the time.

The researchers noted that past studies finding a link between blood clots and the HPV shot were based on a study with few vaccinated participants or another one that did not include comparisons.

This study was published July 8 in a research letter in JAMA. The letter did not note any external funding used. The researchers declared no conflicts of interest.

Review Date: 
July 8, 2014