THE first vaccines designed to prevent cancer could be on the market within a few years. But deciding who should receive the potentially life-saving shots 鈥� and at what age 鈥� could prove controversial.
The vaccines protect against the sexually transmitted virus that causes cervical cancer, which kills almost a quarter of a million women worldwide each year. GlaxoSmithKline has just published the results of phase II trials, which show its vaccine is 100 per cent effective in healthy young women who have the three necessary injections at the right time (The Lancet, vol 364, p 1757).
鈥淭he vaccine acts way, way before you get cancer,鈥� says lead author Diane Harper of the Dartmouth Medical School in Hanover, New Hampshire. 鈥淵ou don鈥檛 get the virus, you don鈥檛 get the precancerous lesions, and we believe the long-term results will show you don鈥檛 get the cancer.鈥�
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Final trials of GSK鈥檚 vaccine are now under way. Rival pharma giant Merck is further ahead; it may apply for US approval of its vaccine as early as next year.
Both vaccines contain proteins that mimic two of the most common strains of the human papillomavirus, HPV16 and HPV18 (快猫短视频, 3 March 2001, p 16). Between them these strains cause 70 per cent of cervical cancers. Merck鈥檚 vaccine also protects against HPV6 and HPV11, which cause genital warts.
It is estimated that 80 per cent of people are infected by HPV at some point in their lives. Most never know they have it, and the immune system usually fights it off within a few months. But in some individuals the infection persists and can eventually turn cells cancerous. In developed countries, screening programmes prevent many deaths, but cervical cancer remains a big killer, especially in poorer countries. The virus may also cause other, rarer cancers, including some kinds of oral and penile tumours.
When HPV vaccines become available, health authorities will face some tricky choices. Cost constraints will probably mean only women are immunised, even though men can carry the virus.
Age is another issue. To be effective, the vaccinations need to be given to girls before they become sexually active. Adding an HPV vaccine to the existing childhood jabs might be the first choice 鈥� but only if immunity lasts at least into adolescence. That will not be known until the trials have been going for longer.
If booster shots are needed, targeting girls before they become sexually active begs the question of when that is 鈥� a highly sensitive issue. 鈥淥nce you start saying you鈥檙e going to vaccinate 12-year-old girls, the press will have a fit,鈥� says Anne Szarewski of Cancer Research UK.
It is also unclear if the vaccines will work for women over 25, on whom they have not been tested. Vaccinating every woman might thus be more expensive than could be justified. Yet trying to limit numbers by, say, excluding those who are already infected, would involve costly tests.
