Review confirms Gardasil's safety; predicted sales hit

Based on the review of available information, the FDA and the Centers for Disease Control and Prevention (CDC) have reaffirmed that Gardasil (quadrivalent human papillomavirus [HPV] types 6, 11, 16, 18 recombinant vaccine) continues to be safe and effective, and its benefits continue to outweigh its risks.

To date, the manufacturer, Merck & Co has distributed over 16 million doses of Gardasil in the US and as of 30th June, there have been 9,749 reports of adverse events following vaccination. Of these, 94 per cent were classified as reports of non-serious events, and 6 per cent as serious events. The non-serious events include syncope, pain at the injection site, headache, nausea and fever.

However, concerns have been raised about reports of deaths occurring in individuals after receiving Gardasil. As of 30th June, 20 deaths had been reported, although there was not a common pattern that would suggest they were caused by the vaccine. According to the review, in cases where autopsy, death certificate and medical records were available, the cause of death was explained by factors other than the vaccine.

Guillain-Barré syndrome (GBS) has also been reported in individuals following vaccination with Gardasil. The FDA and CDC have reviewed the reports and, to date, there is no evidence that Gardasil has increased the rate of GBS above that expected in the population. Thromboembolic disorders have also been reported in people who have received Gardasil. Most of these individuals had risk factors for blood clots, such as use of oral contraceptives, which are known to increase the risk of clotting. Thromboembolic disorders as well as other medical events are being studied through the Vaccine Safety Datalink Project in previously-planned, controlled studies. Merck has also committed to conduct a large post-marketing study to further assess the vaccine's safety.

The vaccine is one of Merck's flagship products but its sales have been under pressure. The company has recently predicted 2008 Gardasil sales of between US$1.4 billion and US$1.6 billion, down from prior estimates of US$1.9 billion to US$2.1 billion. The lower forecast is due, in part, to Merck's failure earlier in the year to receive US approval to market the vaccine to older women aged 27 to 45 years, as well as to extend its indication to include HPV types not included in the vaccine.

Gardasil is approved in the US for use in girls and women aged nine through 26 years to prevents infection with the types of HPV that cause most cases of cervical cancer and genital warts. The CDC's Advisory Committee on Immunization Practices recommended routine three-dose vaccination of girls aged 11 and 12 years. The vaccine is also recommended for girls and women aged 13 through 26 years who have not yet been vaccinated or who have not received all three doses.

Gardasil is marketed by sanofi pasteur MSD (sanofi-aventis’ joint venture [JV] with Merck) in EU countries covered by the JV and several other European countries. In the remaining European countries, located in Central and Eastern Europe, the vaccine is marketed by Merck Sharp & Dohme under the tradename, Silgard.

Matthew Dennis - Editor, Cancer Drug News