The Government is set to save up to £18.6m a year by choosing the Cervarix cervical cancer jab over Gardasil, experts said today.

An announcement last month by the Department of Health sparked controversy after it opted for Cervarix for a UK vaccination campaign for young girls.

Cervarix, made by GlaxoSmithKline, guards against two strains of the HPV virus - 16 and 18 - which cause 70% of cases of cervical cancer.

Gardasil, made by Merck & Co and Sanofi Pasteur MSD, protects against strains 16 and 18, and against strains 6 and 11, which cause lesions and genital warts.

Today, a study published in the British Medical Journal (BMJ) outlined the mathematical model used by the Government and its independent advisory body, the Joint Committee on Vaccination and Immunisation (JCVI), to help it make a decision.

The authors estimated that Cervarix (the bivalent vaccine) must cost £13 to £21 less per dose to be as cost effective as Gardasil (the quadrivalent vaccine).

However, Cervarix does not protect against genital warts, they added.

An accompanying editorial predicted the Government would save £11.5m to £18.6m from the cost of Cervarix alone in the first year of the programme.

Last month, campaigners accused the Government of "saving pennies to spend pounds later" by not choosing Gardasil, which also protects against genital warts.

Cervarix will be given to girls aged 12 and 13 from this September in an attempt to cut the number contracting human papillomavirus (HPV), which causes most cases of cervical cancer.

A catch-up campaign has also been put in place for girls up to the age of 18.

Both GSK and Sanofi Pasteur MSD entered a closed bidding process and the Department of Health has said the costs involved are "commercially confidential".

Mark Jit, health economist and mathematical modeller, Yoon Hong Choi, mathematical modeller, and John Edmunds, head of modelling and economics unit at the Health protection Agency (HPA), compiled today's study.

They said the catch-up campaign for girls was likely to be cost effective but agreed with the JCVI that vaccinating boys would not be a good use of resources.

They concluded: "A bivalent vaccine with the same efficacy against humanpapillomavirus types 16 and 18 costing £13-£21 less per dose (depending on the duration of vaccine protection) may be as cost effective as the quadrivalent vaccine although less effective as it does not prevent anogenital warts."

Strains 6 and 11 are linked to at least nine in 10 cases of anogenital warts.

In an accompanying editorial, Professor Jane Kim, from the Harvard School of Public Health in the US, said the Department of Health seemed willing to forgo health benefits from averting cases of genital warts in return for the reduced cost of Cervarix.

She said: "Because the quadrivalent vaccine protects against genital warts caused by human papillomavirus types 6 and 11, to be equally cost effective the bivalent vaccine must be less expensive.

"The authors estimate that the bivalent vaccine must be £13 to £21 less expensive per dose than the current price of the quadrivalent vaccine.

"Assuming 80% coverage of current 12-year-old girls in the UK with the full three dose vaccine series, this price differential translates to savings of £11.5m to £18.6m from the vaccine price alone in the first year of the programme, compared with adopting the quadrivalent vaccine.

"The decision to select the bivalent vaccine implies that the Department of Health is willing to accept foregone health benefits (and additional cost savings) from averting cases of genital warts for the reduced financial outlay, which may be allocated to other priority investments in health."

A previous study in the BMJ reported encouraging uptakes of first and second doses of the vaccine, but it is unclear what the uptake rates will be for the three-dose series, she added.

A spokeswoman for GSK said the HPA model assumed that the HPV vaccines were both equal in terms of quality and duration of protection against HPV strains 16 and 18.

"It also assumes that protection must last 10 years or longer to make the vaccination programme cost effective.

"There is as yet no data on HPV vaccine response in this period - however GSK's vaccine data has demonstrated prevention of pre-cancerous lesions and strong and sustained immune response for 6.4 years. This is the longest duration of protection reported for any vaccine against HPV 16 and 18.

"Cervarix has been designed specifically to protect against cervical cancer and contains the innovative adjuvant AS04. This adjuvant boosts the body's own immune response to the vaccine, providing a stronger immune response to HPV 16 and 18, compared to the vaccine formulated with a more conventional adjuvant."

A spokeswoman for the Department of Health said: "The contract has been awarded for the vaccine that scored best overall against a number of pre-agreed criteria and offers best overall value to the NHS.

"The vaccination programme has always been about cervical cancer protection, irrespective of which vaccine was chosen. We chose the vaccine that best met this need."

The vaccination programme is aimed at revolutionising the approach to beating cervical cancer, which kills more than 1,000 women in the UK each year.

Dr Nicholas Kitchin, UK medical director of Sanofi Pasteur MSD, said it was good that the mathematical model used was now in the public domain.

"The editorial says the benefits of strains 6 and 11 will be forgone for what is presumably a reduced financial outlay.

"That's the decision the Government has taken.

"We obviously regret that because there's additional benefits Gardasil could have offered girls in the UK. Most other countries have gone for Gardasil.

"There's also a broad safety profile, with 26 million doses having been administered around the world."

Natika Halil, director of information at the FPA, said that while supporting the programme, the charity was disappointed Gardasil had not been chosen.

"In terms of sexual health, the Cervarix vaccine is the most expensive option.

"Choosing this vaccine has cost the UK a rare opportunity to protect an entire generation of its young women against genital warts.

"Genital warts is very common, easily transmitted, but can be stubborn to treat and young women are in a high risk group for this infection. We reiterate our disappointment that Gardasil wasn't chosen.

"Genital warts has its own financial cost to the NHS which spends £22m a year treating it, so it will be interesting to see how this has been factored into the cost analysis."

A spokesman from the Health Protection Agency said: "This shows that a vaccination programme to protect young women against cervical cancer is highly likely to be cost-effective in the UK.

"The study involved complex mathematical modelling and examining thousands of scenarios to explore many of the uncertainties that have not been taken into account in previous cost effectiveness analyses.

"Several issues were found to have a strong influence on the possible costs and health gains due to HPV vaccination, particularly how long the vaccine will protect women for, which is still uncertain.

"The economic evaluation detailed in this study was provided to the Department of Health as part of its decision making process."

Lisa Power, corporate head of policy at the Terrence Higgins Trust, said: "The Government has made a decision which appears to be cost-effective but not health-effective.

"What they are basically saying is they think it's cheaper to let people get genital warts and treat them than to prevent them.

"The cost of human misery has not been considered."