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What's the story behind the 'cervical cancer vaccine'?

This week the Welsh Assembly Government announced that its catch-up programme for HPV (human papillomavirus) vaccination is to be sped up, protecting even more young women and girls from the virus that causes most cases of cervical cancer.

Here’s an article taken from the “Behind the Headlines” section of our website, explaining more about the vaccine, and how it is being used to prevent cervical cancer.

HPV vaccination

HPV infection is the cause of vitually all cases of cervical cancer. In October 2007, Health Secretary Alan Johnson announced that girls aged 12-13 in England will be routinely vaccinated against cervical cancer, which started in September 2008.  There will also be a two-year catch up campaign starting in Autumn 2009, for girls up to 18 years old.

The highly successful and comprehensive cervical screening programme will continue as the available vaccines do not protect against all cancer-causing types of HPV. And it will take several decades before their benefits are seen.

The HPV vaccine programme is an exciting development in cancer prevention, and the media has been reporting on the progress of the vaccines for a number of years. The issue is sometimes presented as a controversy because of fears that HPV vaccination will encourage promiscuity among young girls as well as protect them from cervical cancer later in life.

But are the media reports backed up by the facts?

Cervical cancer and HPV

Cervical cancer is one of the most common cancers diagnosed in women. Almost half a million women around the world are diagnosed with cervical cancer every year and there are over 270,000 deaths each year due to the disease. In the UK, it is the 12th most common form of cancer in women, with around 2,800 cases and just over 1,000 deaths from cervical cancer each year.

Almost all cases of cervical cancer are caused by infection with the human papillomavirus (HPV), although infection doesn’t necessarily mean a woman will get the disease. There are more than 100 different types of HPV. The viruses live on the skin and the lining of body cavities. A number of them infect the genital area and can be spread through skin-to-skin contact, including sexual intercourse. Some types of HPV cause warts; some other types are ‘high risk’ for cervical cancer. These include HPV 16 and HPV 18.

It is thought that the majority of women will be infected with HPV at some point in their lives. In most cases, the immune system fights off this infection without any ill-effects. However, if the infection persists or if a woman is frequently re-infected with any of the high risk types, she is at a higher risk of developing changes in cervical cells that can lead to cervical cancer.

It is not known exactly how HPV infection causes these changes in cells, and it’s a question that Cancer Research UK-funded scientists are working on. But we do know that some proteins produced by the viruses can turn off genes that normally control the function and division of cells. This leads to uncontrolled cell division, a characteristic of cancers.

The HPV vaccines

The vaccines are made of “virus-like particles”. These are the outer shell of the virus with no genetic material inside – they are “dead” viruses. They look like HPV, they feel like HPV, but they cannot infect like HPV.

Their purpose is to teach the immune system what the virus looks like, so it can quickly recognise and destroy it before the person has any ill effects from the infection.

Two HPV vaccines have been developed so far. Gardasil is produced by Merck, while Cervarix (the vaccine being used in the UK) is produced by GlaxoSmithKline.

It is important to note that neither vaccine protects against all the versions of HPV that are associated with the development of cervical cancer. So not all cases of cervical cancer will be prevented. However, studies have shown that each vaccine is 100 per cent effective against the HPV strains that it targets. Both target HPV types 16 and 18: these are responsible for around 70 per cent of cervical cancers. So the current vaccines have the potential to prevent up to 7 out of 10 cases of cervical cancer.

Gardasil also targets HPV types 6 and 11, which are responsible for the majority of cases of genital warts, so it should protect against genital warts as well as most cervical cancers. Cervarix may protect against other strains of HPV that cause up to a further 10 per cent of cervical cancers.

Why do we need an HPV vaccine programme?

Cancer Research UK welcomed the Government’s decision to introduce an HPV vaccination programme. Dr Lesley Walker, the charity’s director of cancer information, said: “This announcement is an important step forward in preventing more cases of cervical cancer. Studies suggest that the vaccine can prevent the majority of cervical cancers.”

It’s important to remember that cervical cancer rates are already low in the UK thanks to the success of the screening programme. A Cancer Research UK study showed that the cervical screening programme could be saving around 5,000 lives every year.

Cervical smear tests are designed to pick up pre-cancerous changes in cells of the cervix. Any abnormal cells can then be removed in order to prevent them developing into cervical cancer.

But there are still around 2,800 cases of cervical cancer diagnosed in the UK every year. By preventing infection with the HPV virus in the first place, rather than treating the symptoms of infection, the majority of these cases could be prevented.

The benefits of using the vaccine include:

  • cutting the number of cases of cervical cancer
  • preventing many of the pre-cancerous conditions that lead to cervical cancer and therefore reducing the need for surgery or other procedures to deal with these
  • reducing the anxiety and trauma experienced by women waiting for the results of a suspected abnormal smear test

So does HPV vaccination mean the end of smear tests? Unfortunately not. There are a number of reasons why it will still be necessary for women to have smear tests, at least in the medium-term:

  • not all women will receive the vaccine
  • the vaccines developed so far do not protect against all the strains of HPV that are associated with the development of cervical cancer, so not all cases of cervical cancer will be prevented
  • there is no evidence to show that the vaccine is effective against cervical cancer in women already infected with HPV, so these women will need to continue smear tests. An ongoing study is investigating the effects of Cervarix when it is given to women over the age of 26 (those more likely to already be infected with HPV)

For the time being it’s vital that women take up the invitation to go for a smear test.

Making the most of the HPV vaccine
For the vaccination to be most effective, it has to be given to people before they are exposed to the virus. Because the main route of transmission of the HPV strains that cause cervical cancer is through sexual intercourse, it needs to be given before a person becomes sexually active.

The current data on Cervarix shows that it gives protection for at least five years.  There is no evidence yet as to how long the protection will last beyond that, so it’s possible that booster injections may be needed.

Some people have suggested that boys should also be vaccinated. It is possible that vaccinating males will have health benefits for them, preventing genital warts and rare genital cancers such as penile and anal cancer, which can also be caused by HPV infection. It is also possible that vaccinating boys/men will have indirect health benefits for girls/women, by reducing the likelihood of infection.

However, we don’t yet know if the vaccine is effective in boys or men. Studies are underway to find out if the vaccine prevents HPV infection and disease in men. When more information is available, vaccination may be licensed and recommended for boys as well.

Is it controversial?
Because of the link some people make between sexual promiscuity and HPV infection, some sections of society may be reluctant to accept HPV vaccination. Some groups have suggested in news articles that giving girls HPV vaccinations will encourage under-age sex and promiscuity.

However, in a survey carried out by Cancer Research UK scientists, 75 per cent of mothers said they want their daughters to receive the HPV vaccination. Only a small minority of mothers were worried that the vaccination would encourage promiscuity.

Some mothers said they were concerned that the HPV vaccine would have side effects. In studies of Gardasil, no serious side effects were reported. The most commonly reported side effects were pain, swelling and redness at the site of injection. A few patients experienced fever, nausea and dizziness. However, these are minor side effects, common with many vaccinations.

Like all vaccination programmes, parents will be able to opt out of vaccination for their daughters, but this would reduce the overall effectiveness of the vaccination programme.

The future
Because there is a 10–20 year gap between HPV infection and development of cervical cancer, it will take some years before the introduction of the HPV vaccine has a major effect on the number of cases of cervical cancer. But the development of the vaccines has given us a fantastic opportunity to prevent the development of the majority of cases of cervical cancer, and, in turn, reduce the number of deaths from the disease.

Anthea Martin

This article was first published in the Behind the Headlines section of our website. We have now moved this content to the blog.

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References:
J PETO, C GILHAM, O FLETCHER, F MATTHEWS (2004). The cervical cancer epidemic that screening has prevented in the UK The Lancet, 364 (9430), 249-256 DOI: 10.1016/S0140-6736(04)16674-9

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