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Gardasil Cervical Cancer Vaccine 99-100% Effective After Three Years: Presented at AACR

By Ed Susman

LOS ANGELES, CA -- April 18, 2007 -- Three years after treatment with the quadrivalent human papillomavirus (HPV) vaccine Gardasil, one woman out of 5,305 who received the vaccine may have become infected with virus that causes cervical cancer, researchers said here at the centennial meeting of the American Association for Cancer Research (AACR) annual meeting.

"That is an interesting case because the infection with [HPV] type 16 was only detected once in four tests, while type 52, another strain linked to cervical cancer, was seen in all four tests," said Darran Brown, MD, professor of medicine, microbiology and immunology, Indiana University School of Medicine, Indianapolis, Indiana, United States.

The vaccine was otherwise 100% effective over three year for protecting women against infection from the more common types 16 and 18 -- believed to cause 70% of cervical cancer worldwide.

"We think this case might have been some form of laboratory or human error," Dr. Brown said, "because it only appeared in one test and then disappeared. However, because it was seen, it was counted as an infection."

The HPV vaccine study, which encompassed 12,167 women, age 16 to 23, was one of two phase 3 trials that led to FDA approval of the vaccine, developed and manufactured by Merck & Co., Inc.

"The high degree of efficacy and safety of this vaccine is remarkable," said Dr. Brown in his presentation of the study results on April 17^th.

The quadrivalent vaccine was designed to protect against four types of HPV: types 6 and 11, which cause genital warts, and 16 and 18, which account for nearly 70% of all cervical cancers. According to Dr. Brown, HPV 6 and 11, while not oncogenic, were included in the vaccine since they cause genital warts and may also cause abnormal results on Papanikolaou smears, leading to expensive and sometimes unnecessary follow-up tests and treatments.

The vaccine also proved highly effective against cervical intraepithelial neoplasia grades 2 and 3, precancerous cervical lesions that are frequently caused by HPV type 16.

While the one disputed case was the only person in the study to be infected with type 16 or 18, Dr. Brown noted that 42 women in the placebo group of patients were infected with the virus types 16 or 18. The difference was highly statistically significant (P < .0001).

The vaccine works by triggering the patient's immune system to produce antibodies to viral proteins analogous to those produced on the surface of each of the four types of HPV. These antibodies, in turn, should offer lasting protection against subsequent natural infection by any of the four types.

"We have not seen a falloff in antibodies triggered by the vaccine," he said. He also said that the vaccine appears to neutralize types 31 and 45, oncogenic types related to types 16 and 18. This research, in parallel to the ongoing study, is examining the quadrivalent vaccine's cross-protective effects against the viruses that cause the remaining 30% of cervical cancer cases.


[Presentation title: High Sustained Efficacy of a Prophylactic Quadrivalent Human Papillomavirus (HPV) (Types 6, 11, 16, 18) L1 Virus-Like Particle (VLP) Vaccine Against Cervical Intraepithelial Neoplasia (CIN) grades 2/3 and Adenocarcinoma in situ (AIS): Abstract LB-187]

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