The discovery and development of the human papillomavirus (HPV) vaccine has been a major breakthrough in public health. There are close to a hundred strains of HPV, some of which cause certain forms of cancer, and about 75% of sexually active men and women have an HPV infection at some point in their lives.
HPV vaccines have been in use for nearly 10 years, and in that time, we have already seen fewer women developing abnormal cervical tissue changes, the first step in cervical cancer. But there is an opportunity to make the vaccines even better and potentially prevent even more HPV infection and HPV-associated cervical cancer cases.
HPV vaccines protect against cancer-causing strains
The first HPV vaccines to have been developed protect against the 2 strains that cause about 70% of all cases of cervical cancer, HPV16 and HPV18. One of these vaccines (Gardasil) also includes the strains HPV6 and HPV11, which are associated with genital warts. It is known as a quadrivalent HPV (qHPV) vaccine.
Researchers then developed a new version of the vaccine that protects against 9 strains of the virus, known as a 9vHPV vaccine (Gardasil 9). It includes the 4 strains (6, 11, 16 and 18) included in the original Gardasil vaccine, along with 5 additional strains that also are associated with cervical cancer. Altogether, researchers estimate that the 9vHPV vaccine could prevent about 90% of cervical cancer cases.
To understand whether the new 9vHPV vaccine is safe and effective, researchers conducted a clinical trial directly comparing 9vHPV vaccine with the qHPV vaccine currently in use, and they found some very promising results.
Clinical trial compared 2 different forms of vaccine
More than 14,000 young women (age 16-26) from 18 different countries participated in the study and received either the new 9vHPV vaccine or the original qHPV vaccine. The researchers monitored the women for up to 6 years after the first vaccination, checking for abnormal cervical cells or disease and studying the immune system’s response to the vaccine.
The researchers found that the new vaccine was highly effective at preventing infection and disease. The vaccine reduced gynecological disease at risk of becoming cancerous related to the 5 additional HPV strains by 97%. In addition, the new vaccine was just as effective as the qHPV vaccine in triggering long-term immune protection against the original 4 HPV strains.
Importantly, the researchers found that most cases of cervical disease diagnosed during the study were in women who had an HPV infection before they were vaccinated, demonstrating the importance of vaccinating women before they are exposed to HPV.
Cervical cancer is a global problem
Current HPV vaccines are effective in reducing infection and high-risk cervical changes, and now there may be opportunity to protect against even more cancer-causing strains. The recent trial shows that the new vaccine is safe and effective in preventing high-risk cervical disease.
Most cases of cervical cancer are diagnosed in low and middle income countries, where access to HPV vaccines and regular screening may be more limited. To have the most impact on cervical cancer globally, prevention measures need to be accessible to these populations. A vaccine that prevents infection from 9 different strains of HPV has enormous potential to prevent cancer around the world, and it is sure to be studied more in the global context.
Eileen Hoftyzer, BSc, and Carolyn Goard, PhD