US regulators have agreed to grant Merck & Co’s cervical cancer vaccine Gardasil priority review status for expanded use in women aged 27-45 years, which means the drugmaker will have a decision within six months.

Gardasil has been on the market since 2006 after the US Food and Drug Administration cleared its use in females aged nine to 26 and, with sales of $1.3 billion last year, has quickly become a big earner for Merck.

Now the company is seeking to expand its use for the older age bracket on the basis that women remain at risk from becoming infected with the human papillomavirus - which is responsible for the majority of cervical cancer cases and other diseases such as genital warts - throughout their lifetime.

The submission is based on clinical data from an international study which showed that Gardasil prevented 91% of cases of persistent infection, low-grade cervical abnormalities and pre-cancers and external genital lesions caused by HPV types 6, 11, 16 and 18 compared with placebo in women aged 24 through 45, clearly demonstrating its potential benefit to this age group.

Gardasil is currently the only cervical cancer vaccine approved in the US - where 6.2 million men and women become infected with HPV every year and around 20 million people are currently infected - but it could soon face competition from GlaxoSmithKline’s rival Cervarix, which hit a stumbling block last December when US regulators asked for more information on the drug.