A major review of studies involving 73,000 women worldwide shows the HPV vaccine was both effective and safe at protecting women against pre-cancerous cervical lesions.

Cochrane Review, released today said its analysis of the 26 international studies also found the risk of serious side effects were the same for women in both the control groups (who received the placebo vaccine) and those who received the actual HPV vaccine. The review conclude that the HPV vaccine effectively protects young women against cervical lesions, that can lead on to cervical cancer, particularly when given between the ages of 15 and 26.

Associate Professor Niki Turner, the director of the Immunisation Advisory Centre, said the review provided no surprises. “As we have seen now from countless studies the vaccine is highly effective against the precursors of cervical cancer when used in adolescents or younger woman. The language here is ‘high certainty evidence’.”

New Zealand started offering the Human papillomavirus (HPV) vaccination to girls at age 12 in 2008 and this was extended to boys last year.

The team of Cochrane researchers summarized 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 studies were well-designed, randomising the women to either HPV vaccine or a placebo.

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 review found that 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 does not appear to increase the risk of serious side effects which was about 7% in both HPV vaccinated or control groups. The researchers did not find increased risk of miscarriage in women became pregnant after vaccination. However, they emphasize that more data are required to provide greater certainty about very rare side effects and the effect vaccines have on rates of stillbirth, and babies born with abnormalities in those who became pregnant around the time of vaccination.

Background

Most people who have sexual contact at some point in their life will be exposed to the human papilloma virus (HPV). In the majority of women, HPV infection will be cleared by the immune system. When the immune system does not clear the virus, persistent HPV infection can cause
abnormal cervical cells. These lesions are known as cervical ‘precancer’ because over time they can progress to cervical cancer if left untreated. There are many different types of HPV. Some are associated with the development of cervical lesions that can become cancerous and are considered as high-risk HPV types.

Two of these high-risk types (HPV16 and HPV18) account for about 70% all cases of cervical cancer worldwide. Vaccines have been developed that help the immune system to recognize certain HPV types. Because cervical cancer can take several years to develop, regulatory bodies and international health agencies such as the World Health Organization (WHO) regard cervical lesions as the preferred outcome measure for HPV vaccine trials.

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