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Merck's new quadrivalent vaccine against human papillomavirus (HPV) was highly effective against precancerous cervical lesions and anogenital warts in two recent trials. In young women not infected with the vaccine serotypes, vaccine efficacy was 90-100% in both trials over three years. However, the vaccine was much less effective in unselected women, some of whom were already infected or had HPV related disease.
The vaccine targets serotypes 6, 11, 16, and 18. Types 6 and 11 cause anogenital warts and some low grade neoplastic lesions. Types 16 and 18 cause most cervical cancers worldwide.
The trials have reignited the debate about who should be vaccinated and when (pp 1905-8, pp 1908-10, pp 1990-1, pp 1991-3). HPV vaccines are most needed in the developing world, where 80% of deaths from cervical cancer occur, says one commentary. But the cost of $360 (£181; €266) is probably beyond the reach of most low income countries.
In countries that can afford it, the vaccine has become a political problem rather than a public health one, says another commentary. Scientists should keep a cool head and continue to look for answers to the remaining questions. We still don't know enough about long term safety, how long immunity will last, the optimum number of doses, or whether other potentially oncogenic HPV serotypes will take over when types 16 and 18 have been eliminated.