New research out of Denmark has found no association between Gardasil – the vaccine that protects against human papillomavirus (HPV) – and an increased risk of venous thromboembolism (VTE), or blood clots.
The findings, published in the Journal of the American Medical Association, alleviate safety concerns that had been raised about the vaccine after two earlier studies reported a potential link.
"Early American studies, which were based on reports coming in from people who were vaccinated, had suggested that there may be an increased chance of blood clots occurring after HPV vaccination," explains Dr Julia Brotherton, epidemiologist and Medical Director of the National HPV Vaccination Program Register.
"This large study based on 5 years of vaccination in the Danish population very elegantly analyses this issue and robustly refutes the presence of any association between HPV vaccination and blood clots," says Brotherton
Professor Basil Donovan, Head of the Sexual Health Program at The Kirby Institute at the University of NSW describes the research as "excellent and rigorous".
"Using a massive population database of 1.6m women, of whom 0.5m had received the HPV vaccine, [Danish researchers] demonstrated no increase in VTE in women in the 42 days after HPV vaccination. The researchers carefully controlled for other VTE risk factors such as pregnancy, oral contraceptives, age, major surgery, and recent cancer," Donovan says.
Professor Michael Quinn, Professor of Gynaecology and Gynaecologic Oncology at the University of Melbourne, says "HPV vaccination has been halted in some countries like Japan because of anxiety about side effects. These results are very reassuring and in keeping with the WHO on this vaccine's safety."
"Australian parents can continue to support the vaccination of their daughters and sons through our world leading HPV vaccination program with confidence," adds Brotherton.
"Though there was an initial wave of reports of adverse events when the HPV vaccination program was first launched in 2007 in Australia, those reports have subsequently dropped to a low level. Based on our current level of knowledge this is a very safe vaccine, but we should keep an open mind," concludes Donovan.
HPV vaccine facts
According to Cancer Council NSW:
- HPVs are the major cause of cervical cancer in women. Genital warts and some cancers in males are related to HPV, including most anal cancer.
- Gardasil is the HPV vaccine currently available in Australia. It prevents infection with HPV types 16, 18, 6 and 11. HPV 16 and 18 are responsible for the majority (70% internationally; 80% in Australia) of cervical cancers. HPV 6 and 11 are responsible for 90% of genital warts.
- The vaccine is most effective if given to girls and boys before the start of sexual activity and therefore exposure to HPV.
- Under the National Immunisation Program Gardasil is free for all 12- and 13-year-old children in a school-based program. A catch-up program for boys aged between 14 and 15 years is available until December 2014.