Sarah Chapman from Cochrane UK blogs about new Cochrane evidence on the safety and effectiveness of HPV vaccination for women to prevent cervical cancer and precancer.
New Cochrane evidence published yesterday shows that vaccinating young women against human papilloma virus (HPV) does, as hoped, reduce the risk of cervical lesions (‘precancer’). HPV vaccines also appear to be safe. These findings, backed by high quality evidence, are reassuring both for those who have already been vaccinated and those needing to make choices about whether to have it.
What is HPV and why does it matter?
Human papilloma viruses are sexually transmitted. Common in young people, most people who have sexual contact at some time in their lives will be exposed to HPV. In most women, the immune system will clear the virus within a few months. In some, this doesn’t happen, and persistent infection with HPV can cause abnormal, ‘precancerous’ cells that may progress to cancer of the cervix (neck of the womb) if left untreated.
Cervical cancer is the fourth most common cancer in women worldwide, primarily affecting younger women. About 70% of all cervical cancers are caused by two high-risk types of the virus, HPV16 and HPV18. Vaccination before exposure to a virus triggers the immune system to produce antibodies, which protect against infection if the person is exposed to it.
Who is vaccinated against HPV?
In the UK, all girls can be vaccinated against HPV free on the NHS, from the age of 12 up to their 18th birthday, and in England girls aged 12 to 13 are routinely offered it in school. Here, take-up is high, but in Denmark, Ireland and Japan confidence in HPV vaccination has plummeted, following alleged cases of neurological problems and parental fears that vaccinating their daughters could encourage promiscuity. In Japan, vaccination take-up has fallen from more than 70% to less than 1%.
Just for girls?
Infection with HPV matters for boys and men too, with HPV types 16 and 18 linked to cancers of the mouth, throat, penis and anus. Vaccinating girls helps in that they won’t be passing on HPV, but this still leaves many men unprotected, including those who have sex with men. The Cochrane Review explores the protection offered to women from cervical precancer, but there are increasing calls for boys to be vaccinated too, with some people paying for the vaccine. Last month saw the start of a phased roll-out of a programme in England to offer HPV vaccination to men who have sex with men through sexual health and HIV clinics. This is already offered in other parts of the UK.
New evidence on HPV vaccination and cervical precancer
The new Cochrane Review brings together evidence from 26 studies with over 73,000 women. The majority were under 25 years old, but three studies involved women aged between 25 and 45. Women in the studies were randomly allocated to receive one of two sorts of HPV vaccine targeting HPV 16/18 or a placebo. There were no eligible studies of a newer vaccine that targets nine HPV types.
None of the studies have followed up their participants for long enough to show whether vaccination has had an effect on cervical cancer. Instead, data are available on the development of cervical lesions between three and a half to eight years after vaccination.
The evidence showed that:
- HPV vaccination in young women aged 15 to 26 reduces the risk of cervical precancer associated with HPV 16/18 from 341 to 157 in 100,000 women, and for any precancer lesions from 559 to 391 in 100,000. This is high-certainty evidence.
- In women vaccinated between 25 and 45 years, the vaccine works less well, possibly because older women are more likely to have been exposed to HPV. The risk of precancer associated with HPV 16/18 is probably reduced from 145 in 10,000 unvaccinated women to 107 in 10,000 following vaccination. The risk of any precancer is probably similar between the two groups. This is moderate-certainty evidence.
- The risk of serious adverse events is similar with HVP and control vaccines (placebo or vaccine against other infections). This is high certainty evidence.
- HPV vaccination probably does not increase the risk of miscarriage but more data are needed about the effects on pregnancy outcomes and very rare side effects.
Professor Peter Openshaw, President of the British Society of Immunology, was among a number of scientific experts who were quick to welcome this new evidence. He commented that it “paints a reassuring picture, highlighting the huge public health benefits that this vaccine offers to young women”, and stressed the need to “redouble efforts to ensure that HPV vaccination rates in girls remain high and that we continue to actively communicate the benefits of this vaccine to parents and children”.
Part of a bigger picture
The lead author of the Cochrane Review, Dr. Marc Arbyn, from the Unit of Cancer Epidemiology, Belgian Cancer Centre, Sciensano, 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.”
Screening still matters
Women should remain aware of the importance of screening though, said Dr. Jo Morrison, Consultant in Gynaecological Oncology at the Musgrove Park Hospital, Somerset, UK. “Vaccination aims to prime the immune system to produce antibodies that can block subsequent natural HPV infection. These data show that immunizing against HPV infection protects against cervical precancer, and it is very likely that this will reduce cervical cancer rates in the future. However, it cannot prevent all cervical cancer and it is still important to have regular screening, even if you have been vaccinated.”
My daughters both chose to be vaccinated, a handful of years ago, but as we looked at the information provided to help with their decisions, we were aware that the evidence-base was thin. This Cochrane Review changes that, and should enable young women to make a more informed choice.
References may be found here.
Sarah Chapman has nothing to disclose.