Human papillomavirus (HPV) vaccines provide protection against the development of cervical cancer or cervical lesions in young women who are vaccinated between 15 and 26 years of age, according to a new study published in the Cochrane Library.
The study was conducted by Marc Arbyn, Sciensano, Unit of Cancer Epidemiology, Belgian Cancer Centre, Brussels, Belgium, and colleagues to evaluate the harms and protection of prophylactic human HPV vaccines against cervical precancer and HPV16/18 infection in adolescent girls and women.
People engaging in sexual contact at some point in their life will be exposed to the HPV. In most of the cases, HPV infection gets eliminated through the body’s immune system. But, if the virus is not eliminated by the immune system, persistent HPV infection can cause the development of abnormal cervical cells. These lesions are known as cervical precancer because if left untreated they can progress to cervical cancer.
HPV16 and HPV18, high-risk HPV types that can become cancerous, 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.
For the study, the 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, randomizing the women to either HPV vaccine or a placebo. 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 newer vaccine that targets nine HPV types was not included in the review since it has not been compared against a placebo in a randomized controlled trial.
The review looked at two groups of people: women who are free of high-risk HPV (hrHPV) 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.
- In women free of hrHPV, HPV vaccines reduce the risk of cervical precancer associated with HPV16/18 from 164 to 2/10,000 women and reduce any precancer from 287 to 106/10,000
- In younger women free of HPV16/18, HPV vaccines reduce the risk of precancer associated with HPV16/18 from 113 to 6/10,000 women
- In women free of HPV16/18, who are older than 25, the vaccines reduce the number with precancer associated with HPV16/18 from 45 to 14/10,000
- HPV vaccination reduces the risk of precancer associated with HPV16/18 from 341 to 157/10,000 and any precancer from 559 to 391/10,000, in all young women (15-26) with or without HPV infection
- In older women (25-45) with or without HPV infection, the effects of HPV vaccine on precancer are smaller, which may be due to previous exposure to HPV and risk of precancer associated with HPV16/18 is probably reduced from 145/10,000 in unvaccinated women to 107/10,000 women following HPV vaccination
- The risk of serious adverse events is similar in HPV and control vaccines (placebo or vaccine against another infection than HPV
- HPV vaccines did not increase the risk of miscarriage or termination of pregnancy
- The rate of death is similar overall (11/10,000 in control group, 14/10,000 in HPV vaccine group)
- The number of deaths overall is low although a higher number of deaths in older women was observed
Cochrane lead author, Dr. 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.”
“There is high-certainty evidence that HPV vaccines protect against cervical precancer in adolescent girls and women who are vaccinated between 15 and 26 years of age,” concluded the authors.
The protection is lower when a part of the population is already infected with HPV. Longer-term follow-up is needed to assess the impact on cervical cancer. The vaccines do not increase the risk of serious adverse events, miscarriage or pregnancy termination. There are limited data from trials on the effect of vaccines on deaths, stillbirth, and babies born with malformations.
For further information click on the link: http://dx.doi.org/10.1002/14651858.CD009069.pub3