US health regulators have come out firmly behind Merck & Co’s Gardasil, saying that the cervical cancer vaccine remains safe and effective, despite an analysis earlier this week which cast doubt on the treatment.

The US Food and Drug Administration and the Centers for Disease Control and Prevention (CDC) said that Gardasil “continues to be safe and effective, and its benefits continue to outweigh its risks". The joint statement came in response to an analysis published in the Journal of the American Medical Association, co-authored by the FDA and CDC and based on reports of adverse events to the Vaccine Adverse Events Reporting System, between Gardasil’s launch in June 2006 up to December 2008. It described 12,424 reports of adverse events following vaccination, 772 (6.2%) of which were serious.

The Gardasil safety review assessed a wide range adverse events, including local injection site reactions, fainting, dizziness, nausea and headaches, as well as Guillain-Barre syndrome, venous thromboembolic events and deaths. All of these events are included in the vaccine’s labelling, the FDA and CDC noted, and while a higher proportion of Gardasil reports were of fainting and VTEs compared with other vaccines, none of the adverse events “were reported at rates greater than expected in a population of this age and gender and with other known contributing factors to these adverse events”.

During that time period, Merck distributed over 23 million doses of Gardasil in the USA. Given this number of doses,” it is expected that, by chance alone, serious adverse events and some deaths will be reported”, said the FDA and CDC and indeed 32 deaths have been confirmed. However, "there was not a common pattern to the deaths that would suggest they were caused by the vaccine," the agencies noted.

The FDA and CDC will continue to “closely monitor the safety of Gardasil”, but conclude by saying that the product will “potentially benefit the health of millions of women” by providing protection against the types of human papillomavirus in the vaccine that cause cervical, vulvar and vaginal cancer, genital warts, and other HPV-related genital diseases.