Forecasting the Future of Cervical Cancer: the Wales HPV Baseline Study Ten Years On
This week marks Cervical Cancer Prevention Week, which highlights the fact that every day in the UK two women lose their lives to cervical cancer and nine others receive a life-changing diagnosis.
The week also provides an important opportunity to raise awareness of vaccination against HPV (Human Papilloma Virus) as the most effective way to prevent the incidence of cervical cancer and reduce the burden of the disease in women everywhere.
Cervical cancer is the most frequently diagnosed cancer in women under 35 and is caused by the very common and usually harmless virus HPV. This virus normally lives on the skin and is transmitted by prolonged skin-skin contact, which is why HPV is considered the most common sexually transmitted disease.
There are over 100 different strains of HPV, of which only some are high risk for their ability to cause high-grade cervical disease and cancer. The two main strains that together account for over 70% of all cervical cancers are HPV 16 and 18.
Following HPV infection, the virus is usually eliminated by the immune system of healthy women. However, for reasons that are not completely understood, in some cases the virus can persist and lead to changes in the cells that line the cervix, which left untreated can develop into invasive cervical cancer years later.
When the HPV vaccine was introduced for the first time in 2008, Cancer Research Wales embarked on a major public health study designed to predict the success of the national HPV vaccination programme, by providing an important baseline against which the HPV vaccination programme could be measured in future.
At the time, the study represented the largest of its type to examine the prevalence of HPV in young women within the general population.
The study, led by Dr Sam Hibbitts and Professor Alison Fiander from Cardiff University and in collaboration with Public Health Wales, set out to provide a baseline of HPV infection rates in unvaccinated Welsh women who were called for their first cervical smear between the ages of 20 and 22.
The study analysed the smear samples of over 13,000 women for evidence of HPV infection, revealing some important findings. Significantly, over a quarter of all samples were infected with at least one high-risk strain of HPV with the potential to cause cancer. The main HPV high-risk strains present were found to be HPV 18, 16, 31, 51 and 56, with HPV 16 the most common in single and multiple infections.
Most women would have eliminated the virus within two years following infection as the samples only represent a snapshot in time, but what the finding did highlight was the high prevalence of high-risk HPV strains in the general population.
Furthermore, a small but not insignificant proportion of Welsh women - around 2% --were found to be infected with high-risk HPV strains 51 and 56. This is significant because the current vaccines do not provide protection against these two strains.
Fortunately, in 2018 Wales introduced HPV testing as part of its cervical screening programme, which offers a much more sensitive test for detecting possible changes and risk, thus reducing the impact that these two strains may cause.
If following routine testing the sample provided proves to be HPV negative, then women will be invited back after 5 years, instead of the usual 3 years, as the risk of developing cervical cancer is low.
The information gathered by the pivotal Cancer Research Wales HPV baseline study allowed the scientists to model the predicted effectiveness of the HPV vaccination programme.
Assuming 100% protection against the two main targeted high-risk strains (HPV 16 and 18), the scientists were able to predict that the vaccines used at the time would also cross-protect against other non-targeted high-risk strains of the virus by up to 47%.
Overall, the HPV baseline study predicted a dramatic reduction in the future cases of high-grade cervical disease and invasive cervical cancer.
The first schoolgirls to have received the vaccine have now reached the age where they themselves attend cervical screening. Thankfully, the HPV vaccine has lived up to its promise and proved very effective at reducing the incidence of pre-cancerous cervical changes in these women.
Dr Sam Hibbitts
“Reflecting from these early studies, the direction of travel the team anticipated has come into effect. With thanks to Cancer Research Wales for funding much of our research, I hope it has helped to support the significant changes in cervical screening & implementation of the HPV vaccination programme over the last 10 years in the UK.”
In 2012, Gardasil™, which also targets low-risk strains HPV 6 and 11 that cause genital warts, replaced Cervarix as the vaccine of choice for the national HPV vaccination programme in Wales. The early HPV vaccine trials showed Gardasil™ to be 100% effective in preventing high-grade cervical disease.
Despite these encouraging results, Wales must not become complacent as HPV vaccination rates are still below the desired target, with concerning variation in uptake across Wales.
In parts of Blaenau Gwent, Caerphilly, Cardiff, Newport, Conway, Denbighshire, and Torfaen the number of eligible persons that have received at least one HPV vaccine is below the Welsh average of 66%.
Wales has the second highest incidence of cervical cancer out of the devolved nations with 12 cases per 100,000, just behind Scotland. The World Health Organisation have set a target of only four cases of cervical cancer per 100,000 before it can be considered eliminated as a public health concern. This target has been set alongside the aim of achieving 90% of full HPV vaccination in all schoolgirls.
Earlier this month Public Heath Wales launched a publicity campaign to encourage all young persons under the age of 25 to get vaccinated against HPV, as it is the most effective way to protect not only against cervical cancer, but also against several other cancer types that include some head and neck cancers, anal, vulval and vaginal cancers, as covered in our previous blog.
To find out more about the PHW HPV vaccination campaign please go to their website where you will find a series of short informative videos and much more information on the vaccine and those who may be eligible to receive it.