New study reinforces Gardasil's safety

An analysis of the adverse events (AEs) reported following distribution of Merck & Co's quadrivalent human papillomavirus (qHPV) recombinant vaccine, Gardasil, since 2006, has indicated that AE rates were consistent with prelicensing data and expected background rates of other vaccines, with the exception of a higher proportion of reports of fainting and blood clots.

Gardasil is the world's first cervical cancer vaccine, which can also help to prevent vulvar and vaginal cancers and genital warts caused by HPV types 6, 11, 16 and 18. In June 2006, the FDA licensed Gardasil for females aged nine to 26 years to prevent infection with genital HPV. Shortly after that, the Advisory Committee on Immunization Practices recommended routine vaccination of females aged 11 to 12 years with three doses of qHPV and catch-up vaccination for females aged 13 to 26 years.

In the new study, published in the 19th August issue of JAMA (2009;302:750-757), the researchers analysed reports of AEs following qHPV immunisation received by the Vaccine Adverse Event Reporting System (VAERS) from 1st June 2006 until 31st December 2008. Additional analyses were performed for some AEs following immunisations (AEFIs) in prelicensure trials, those of unusual severity or those that had received public attention.

During the study period, VAERS received 12,424 reports of AEFIs following receipt of qHPV, an overall reporting rate of 53.9 reports per 100,000 vaccine doses distributed. Of the 8,247 reports that included onset interval, 4,393 (40 per cent) occurred on the day of vaccination. Among 9,396 reports (77 per cent) with dose information, 5,772 (61 per cent) followed the first dose, 2,380 (25 per cent) followed the second dose and 1,183 (13 per cent) followed the third dose of qHPV.

Among the 12,424 AEFI reports, 772 (6.2 per cent) were serious, including 32 reports of death. The reporting rates per 100,000 qHPV doses distributed were: 8.2 for syncope; 7.5 for local site reactions; 6.8 for dizziness; 5.0 for nausea; 4.1 for headache; 3.1 for hypersensitivity reactions; 2.6 for urticaria; 0.2 for venous thromboembolic events, autoimmune disorders and Guillain-Barré syndrome; and 0.1 for anaphylaxis and death. Analysis indicated a disproportional reporting of fainting and blood clot events.

The VAERS database that was the primary source for the study is one of the many mechanisms used to assess the safety of vaccines. Merck also monitors vaccine safety by conducting comprehensive analyses of AEs reported to the company and shares these analyses with the Centers for Disease Control and Prevention (CDC), the FDA, and regulatory and medical authorities around the world to support their efforts. After carefully reviewing all of the information available to Merck about reported AEs, including the findings in the discussed study, the company continues to be confident in the safety profile of Gardasil. While no vaccine or medicine is completely without risk, leading health organisations throughout the world, including the CDC and EMEA, have reviewed the available safety and efficacy information about Gardasil and continue to recommend its use.

Richard M Haupt, head of the Gardasil clinical programme commented: "we will continue our practice of effectively communicating the safety profile of Gardasil, it's a responsibility Merck takes very seriously...Parents should understand the extensive data supporting the safety profile of this vaccine, and we encourage them to look to CDC and FDA, and to the advice of their own physicians, to make an informed choice about something as important as a vaccine to help prevent cervical cancer".

Alice Rossiter Cancer Drug News Editor