A recent study has found that the human papilloma virus (HPV) vaccines protect against cervical cancer in young women.

A team of Cochrane researchers has summarised results of 26 studies in 73,428 women conducted across all continents over the last eight years. Most women in the studies were under the age of 26 years old, although three trials recruited women between 25 and 45 years. The review evaluates evidence for two vaccines: the bivalent vaccine targeting HPV16 and 18, and the quadrivalent vaccine targeting HPV16/18 and two low-risk HPV types causing genital warts.

The review looked at two groups of people: women who are free of high-risk HPV at the time of vaccination and all women regardless of HPV status at vaccination. The effects of the vaccine were measured as precancer associated with HPV16/18 and precancer irrespective of HPV type. The review looked at data from ten trials assessing cervical lesion data at between three and a half to eight years after vaccination.

None of the studies have followed up participants for long enough to detect an effect on cervical cancer. The researchers looked at precancer cervical lesions instead. They found that in young women who did not carry HPV, vaccination reduced the risk of developing precancer. About 164 per 10,000 women who got placebo and 2 per 10,000 women who got the vaccine went on to develop cervical precancer.

The researchers also looked at data from all enrolled women regardless whether they were free of high-risk HPV at vaccination or not. Among women aged 15 to 26 years, vaccines reduced the risk of cervical precancer associated with HPV16/18 from 341 to 157 per 10,000. HPV vaccination reduced also the risk for any precancer lesions from 559 to 391 per 10,000.

In older women vaccinated between 25 to 45 years the HPV vaccine does not work as well. This might be because older women are more likely to have been exposed already. The evidence also shows that the vaccines do not appear to increase the risk of serious side effects which was about 7% in both HPV vaccinated or control groups.

Cochrane lead author, Dr. Marc Arbyn, said: "The findings of this review should be viewed within the context of multiple global surveillance studies, which have been conducted by the Global Advisory Committee on Vaccine Safety from the WHO since the vaccinations were licensed. The committee concluded that the risk-benefit profile of prophylactic HPV vaccines remains favourable and expressed its concerns about unjustified claims of harm that lack biological and epidemiological evidence, and which may affect the confidence of the public. At the same time, the Committee encouraged health authorities to continue surveillance and examination for potential adverse events." The study has been published today in the journal Cochrane Library.