Gardasil, a vaccine designed to prevent the development of cervical cancer, should be approved for marketing in girls as young as nine, according to a committee of experts convened by the US Food and Drug Administration.

The panel voted unanimously in favour of the vaccine, developed by Merck & Co, saying it was clearly effective in preventing infection with human papillomavirus, which can lead to premalignant lesions of the cervix, cervical cancer and genital warts. But while the efficacy of Gardasil is not in question, the FDA still faces a difficult task deciding exactly who should receive it.

The vaccine has already courted controversy with some groups claiming that vaccinating young girls against HPV – a sexually-transmitted infection – could be taken as an encouragement to become sexually active. The panelists agreed that a widespread vaccination campaign would have significant benefits in reducing the incidence of cervical cancer and other HPV-related diseases, and that it would be preferable to vaccinate girls earlier, before they become sexually-active.

Merck also wants to vaccinate boys aged nine or over, to reduce the circulation of HPV in the population, but the panel did not vote on this issue.

Ahead of the meeting, FDA reviewers published documents asking the panel to look at the risk that Gardasil may actually encourage progression of pre-malignant cervical conditions in women who had already been infected with HPV, but this was not considered to be a reason to block approval. Also, congenital malformations seen in five children born to women who had received the vaccine were considered to be unrelated to the vaccine.

Merck also insisted that Gardasil would not be a replacement for cervical screening. The company has also agreed to do further studies to assess the need for booster injections, to explore how long women can remain protected from infection.

Some observers suggested the anticipated high cost of the vaccine, tipped to be between $300 and $500, could make it hard for governments to fund widespread vaccination campaigns. The US Advisory Committee on Immunization Practices is to decide next month on whether the vaccine should come into routine use.

The FDA is due to rule on the marketing application on or before June 8 and, if its gets the go-ahead, analysts believe Gardasil could become a $3 billion product. A rival product from GlaxoSmithKline called Cervarix, submitted for approval in Europe but not yet in the USA, is expected to reach $2 billion in peak sales.