The vast majority of cervical cancers are caused by an infection with human papillomavirus (HPV), a sexually transmitted virus that almost all sexually active men and women will get during their lifetime. In June of 2006, the US FDA approved a quadrivalent vaccine against HPV that targets four strains of high-risk HPV associated with certain cancers and genital warts.
The quadrivalent HPV vaccine had already been shown to be effective in preventing genital warts and precancerous cervical changes that eventually progress to invasive cervical cancer. What was missing from the equation—until now—was a demonstration that receiving the quadrivalent HPV vaccine lowers the risk of developing cervical cancer.
In a recent study published in the New England Journal of Medicine, a group of researchers in Sweden reported that the quadrivalent HPV vaccine was associated with a reduced risk of cervical cancer.
Due to the time it takes for precancerous lesions to progress to invasive cervical cancer, it is very difficult to design a forward-looking study to demonstrate that the HPV vaccine reduces the risk of cervical cancer. Therefore, this research group used a patient registry to obtain the data for their research. A patient registry is an organized collection of data used to assess outcomes for defined patient populations. Patient registries can be used to evaluate the effectiveness of treatments, understand a disease on a population-wide level, and explore elements that affect the outcome of a disease.
In this study, over 1.6 million girls and women between the ages of 10 and 30 were identified in the Swedish Total Population Register from 2006 to 2017. The researchers followed these girls and women until their 31st birthday to evaluate the risk of invasive cervical cancer in those who received the HPV vaccination during the study period (over half a million girls and women, or 31.6%) compared with those who remained unvaccinated during that time (around 1.1 million participants, or 68.4%).
In the vaccinated group, 19 cases of cervical cancer were diagnosed over the study period, compared with 538 cases in the unvaccinated group. Age at first vaccination has been explored as an important factor in protecting against cervical cancer, and in this study, the majority (83.2%) of the women and girls who were vaccinated received their first dose before age 17. Of these, only 2 were diagnosed with cervical cancer during the study period.
Next, the group performed a risk assessment, which showed 63% lower risk risk of developing cervical cancer in vaccinated girls and women. Interestingly, vaccination at a younger age (under 17 years) further reduced risk, with this group having an 88% lower risk than the unvaccinated group.
Together, the results of this study show that the HPV quadrivalent vaccine is associated with a lower risk of developing cervical cancer, which is the ultimate goal of vaccine implementation. Importantly, this research illustrated that the risk of cervical cancer was even more substantially reduced when the vaccine was first given before age 17. This is consistent with the guidance that vaccination against HPV should be completed before exposure, as the vaccination has no effect on preexisting infections, only new infections.
To learn more about HPV and cervical cancer, check out our previous blog post here.
