The final piece of missing evidence has emerged to prove vaccines against the human papillomavirus (HPV) reduces cervical cancer rates. Until now, numerous lines of research have provided positive indications, but the last essential test was always going to take time.
A report in the Canadian Medical Association Journal has revealed that girls who received the Gardasil vaccination in 2008 are more than a quarter less likely to have cervical abnormalities that can lead to cancer than those who were not vaccinated.
Most cervical cancers are caused by HPV. So when Professor Ian Frazer demonstrated the capacity of artificial “virus-like particles” to produce antibodies against HPV, it was likely vaccines made from these particles could help prevent a disease that kills 270,000 women each year.
However, HPV infections take years to turn cancerous. Frazer's work left health authorities with a conundrum. Waiting to see if the trials of the vaccine reduced cancers would mean leaving tens of millions of girls unvaccinated in the meantime.
The decision was controversial. Gardasil is expensive, and some politicians argued that protection against HPV would encourage teenage promiscuity. Naturally, anti-vaccination advocates jumped on board, publicizing rare cases of negative reactions. Even some medical researchers questioned if the immunity would last.
Early evidence for the effectiveness of the vaccine emerged with the fall in the frequency of genital warts. Like cervical cancer, genital warts are caused by HPV (although usually by different strains), but they take much less time to emerge. Several studies have shown that genital warts are becoming less common wherever vaccination is widespread. Success against warts does not equal success against cancer, but is considered suggestive.