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Long awaited study results have confirmed that the quadrivalent human papillomavirus (HPV) vaccine substantially reduces invasive cervical cancer risk.
Published in the New England Journal of Medicine, the study followed over 1.5 million girls and women in Sweden up to 11 years and found that the risk of cervical cancer by age 30 was 63% lower in vaccinated women compared with unvaccinated women.
Previous studies have confirmed that HPV vaccination, is effective in preventing HPV infection, genital warts, and high-grade precancerous cell changes in the cervix. But as the vaccine was only introduced in the 2000s, until now it hadn’t been possible definitely say the vaccine reduces cases of cervical cancer itself, which is the ultimate goal of the HPV vaccination program.
Professor Jack Cuzick, a Cancer Research UK-funded cancer prevention expert at Queen Mary University of London, commented, “this is an extremely important paper and for the first time documents the impact of the HPV vaccination on the risk of cervical cancer, and not just against HPV infections and precancerous lesions.”
A vaccine to prevent cancer
HPV is a virus that infects the skin and cells lining the inside of the body. It’s an extremely common infection and in most people it doesn’t cause any problems at all. But virtually all cases of cervical cancer are caused by HPV. There are hundreds of different types of HPV, but only around 13 strains are known to be linked to cancer.
Different forms of HPV vaccine
There are various forms of the HPV vaccine that protect against different HPV strains:
- Quadrivalent vaccine (Gardasil): Protects again 4 types of HPV – HPV 16 and 18, which together cause around 7 in 10 cervical cancer cases in the UK, and HPV 6 and 11, which cause most genital warts. This is the vaccine available in the UK to all children aged 11 to 13 and was the vaccine used in this study.
- Bivalent vaccine (Cervarix): Protects against HPV 16 and 18, has the equivalent cancer-prevent properties as the quadrivalent vaccine.
- Nonvalent vaccine: (Gardasil 9): Protects against 9 types of HPV, including types 31, 33, 45, 52 and 58, as well as the HPV types mentioned above.
What did the study find?
Researchers used data from the national Swedish demographic and health registers to look at differences in cervical cancer rates in women who were and weren’t vaccinated.
1,672, 983 girls and women between 10-30 years of age were included in the study, with their records followed up until they were diagnosed with cervical cancer, emigrated from Sweden, died, were lost from the registry, received the bivalent HPV vaccination, or turned 31.
Between 2006 and 2017, 527,871 women had at least one dose of the quadrivalent HPV vaccine and were considered vaccinated.
At the end of the study, 19 women who had received the quadrivalent HPV vaccine and 538 women who had not received the vaccine had been diagnosed with cervical cancer. This translates to 47 cases per 100,000 women who had been vaccinated compared to 94 cases per 100,000 in women who had not been vaccinated. As the study only followed women until they turned 31, these figures only apply to women up to the age of 30.
After adjusting for risk factors, HPV vaccination was responsible for a 63% reduction in cervical cancer incidence.
What’s more, the incidence of cervical cancer was lowest among those who had been vaccinated before they turned 17. Sasieni adds how “the dramatic reduction in cervical cancer in women vaccinated under the age of 17 underlines the value of the school-based HPV immunisation programme.”
Whilst the results are great news for those who have been vaccinated, the vaccine doesn’t protect against all types of HPV and not all age groups have had the opportunity to receive it.
“Cervical screening remains the key to cervical cancer prevention in women who weren’t vaccinated before becoming sexually active,” says Sasieni. This is because cervical screening can spot early cell changes caused by HPV, before they have a chance to become cancer.
Cervical screening is still important for vaccinated women as the vaccines don’t protect against all HPV strains.The UK offers regular cervical screening to women and anyone with a cervix between the ages of 25 and 64.
What was missing?
Whilst the study accounted for factors, such as when someone was vaccinated, there were various factors that weren’t measured. For example, the study didn’t account for the relationship between cervical cancer and environmental factors – such as smoking status, sexual activity and oral contraceptive use.
The study also didn’t look at if people attended cervical screening, which could influence the number of diagnosed cervical cancer cases. Cervical screening is offered to women in Sweden every 3 to 7 years to women, depending on their age.
Despite these gaps, the latest study has been called a “vital milestone confirming the effectiveness of the HPV vaccine”.
“It’s really exciting that we’re beginning to see the great impact it has on reducing cervical cancer incidence and these results are extremely promising,” said Sophia Lowes, Cancer Research UK’s health information manager. “It’s a personal decision whether to have the HPV vaccine, but we would recommend that everyone offered the vaccine take it up.”
Lei, J. et al (2020) HPV vaccination and the risk of invasive cervical cancer. New England Journal of Medicine. DOI:10.1056/NEJMoa1917338