By Julie Steenhuysen

CHICAGO, Sept 1 (Reuters) - Young women in Australia who got a vaccine to prevent cervical cancer were five to 20 times more likely to have a rare but severe allergic reaction than girls who got other vaccines in comparable school-based vaccination programs, researchers said on Monday.

They said the severe allergic reactions to the human papillomavirus or HPV vaccine were unusual and manageable and that the vaccine remained safe.

The team of Australian researchers led by Dr. Julia Brotherton of The Children's Hospital at Westmead studied 114,000 young women vaccinated with Merck & Co's <MRK.N> Gardasil vaccine as part of a 2007 vaccination program in New South Wales.

Of these, 12 had suspected cases of anaphylaxis, a potentially life-threatening allergic reaction that can cause difficulty breathing, nausea and rashes, they reported in the Canadian Medical Association Journal.

Eight out of the 12 young women had confirmed anaphylactic reactions after getting the vaccine, for an estimated rate of reaction of 2.6 per 100,000 doses administered. That compared with a rate of 0.1 per 100,000 doses in a 2003 school-based meningitis vaccination program.

Brotherton and colleagues suspect the higher rates of allergic reaction could be due to better surveillance programs to watch for such reactions, the higher tendency for young women to have such reactions compared with men and an apparent overall rise in the incidence of anaphylaxis in Australia.

Nevertheless, they said that the rates remain rare and should not discourage use of the vaccine, which targets four strains of the human papillomavirus, a common sexually transmitted virus that causes genital warts and most cases of cervical cancer.

"It's just a reminder that there are rare adverse effects," said Dr. Neal Halsey of Johns Hopkins University in Baltimore, who wrote a commentary on the study.

"It doesn't change the strong recommendations for all adolescent girls to get this vaccine but we just have to watch them to make sure they don't have this allergic reaction," he said in a telephone interview.

Last May, the U.S. Centers for Disease Control and Prevention said Gardasil has been associated with a higher risk of fainting, in some cases resulting in injury.

In the United States, Merck has distributed more than 16 million doses of Gardasil, which is approved for women and girls ages 9 to 26.

(Editing by Maggie Fox and David Wiessler)

AlertNet news is provided by