Eighty million doses have been distributed worldwide compared to 25m of Cervarix, which is manufactured by GlaxoSmithKline.

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But Glaxo says Cervarix uses a more powerful technology to spur a response from the immune system--potentially making Cervarix more effective.

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Clinical trials and post-marketing monitoring of Gardasil, made by Merck, and Cervarix, made by GlaxoSmithKline, showed side effects similar to placebo.

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Besides Gardasil, another choice is Cervarix, which is marketed by GlaxoSmithKline.

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Natalie Morton's sudden death Monday occurred within hours after she received a shot of the vaccine Cervarix at the NHS at her school in Coventry.

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When the national immunisation project was announced, there was some controversy about the selection of Cervarix over Gardasil, which is used by the majority of vaccination programmes worldwide.

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GlaxoSmithKline is developing its own cervical cancer vaccine, Cervarix, which some studies show may be even better than Gardasil at teaching the immune system to fight off the virus.

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In a risky move, GlaxoSmithKline says it will conduct a 1, 000-patient clinical trial to test its vaccine to prevent cervical cancer, Cervarix, against a rival product made by Merck.

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The advisory committee also voted that Cervarix, a new HPV vaccine made by GlaxoSmithKline, appeared to be safe and effective for girls and young women 10 to 25 years of age.

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Both Merck's Gardasil, which is already on the market, and Glaxo's Cervarix, which is not, work by preventing infection of strains of the human papilloma virus (HPV) that, in turn, cause the vast majority of cervical cancer cases.

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Cervarix has been approved in Europe.

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Both Merck's (nyse: MRK - news - people ) Gardasil, which is already on the market, and Glaxo's (nyse: GSK - news - people ) Cervarix, which is not, work by preventing infection of strains of the human papilloma virus (HPV) that, in turn, cause the vast majority of cervical cancer cases.

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