Merck & Co has been boosted by the news that US health regulators have approved the firm’s Gardasil vaccine for the prevention of certain vaginal and vulvar cancers.

The US Food and Drug Administration originally approved Gardasil in 2006 for girls and women aged 9 to 26 for the prevention of cervical cancer caused by human papillomavirus types 16 and 18, precancerous genital lesions (HPV types 6, 11, 16, and 18) and genital warts caused by HPV types 6 and 11. Now the agency has backed the jab for vaginal and vulvar cancer caused by HPV types 16 and 18.

The latter two HPV types cause 70% of cervical cancers, and are known to also cause some vulvar and vaginal cancers, “but the percentages are not well defined”, the agency said. Nevertheless, “there is now strong evidence showing that this vaccine can help prevent vulvar and vaginal cancers due to the same viruses for which it also helps protect against cervical cancer," said Jesse Goodman, director of the FDA's Center for Biologics Evaluation and Research. “While vulvar and vaginal cancers are rare (over 5,500 cases are diagnosed in the USA each year), the opportunity to help prevent them is potentially an important additional benefit from immunisation against HPV.”

Merck followed more than 15,000 participants from the original studies for about two extra years. In the control group that did not receive Gardasil, 10 individuals developed precancerous vulvar lesions and nine developed precancerous vaginal lesions, all related to HPV types 16 or 18. No one in the Gardasil group developed either kind of lesion due to the latter, however the FDA warned that "no vaccine is 100% effective" and said that all women should still be screened regularly, even after they have been vaccinated.

The expanded approval means that Gardasil will now have a further advantage over GlaxoSmithKline’s Cervarix which has still not been approved by the FDA. The approval is timely given the adverse news that has been surrounding Merck’s jab of late, following articles in The New England Journal of Medicine which questioned the cost-effectiveness and safety of Gardasil.

Also, Merck has been battling of late to address a slowdown in Gardasil sales of late. It recently started offering doctors free replacement doses if a privately-insured 19- to 26-year-old woman learns that the vaccine is not covered by her policy.