Among the more than 100 types of human papillomavirus (HPV), at least 14 are considered as 'high-risk' types which can cause (cervical) cancer. After breast cancer, cervical cancer is the most common cancer in Europe among women aged 15–44 years [1].
Before HPV vaccination among teenage girls started in Denmark, high-risk HPV was found in all cervical cancers. HPV types 16/18 accounted for around three quarters (74%) of cervical cancers. These two types are covered in the 4-valent HPV vaccine offered to girls since 2008 as well as the 9-valent vaccine which has been in use in Denmark since November 2017. One third (26%) of cervical cancers prior to the HPV immunisation campaign were caused by high-risk types that are not covered by the 2- and 4-valent vaccine.
In their research article published in Eurosurveillance, Nonboe et al. examined the HPV status of cervical samples over time among women (22–30 years) at screening age for cervical cancer who were vaccinated as girls [2].
They tested up to three consecutive cervical cell samples per participant provided by the contributing pathology departments in Denmark for HPV. In total, 17,252 women with at least one cervical cell sample were registered between 1 February 2017 and 29 February 2024. During the seven years of the randomised "Trial23" study (cervical cancer screening starts at age 23 in Denmark), 84% of women in the study had at least one cell sample taken. The authors compared HPV prevalence, persistence and incidence among vaccinated and unvaccinated women.
"Strong indication" of population immunity against high-risk HPV types 16 and 18
Based on the data gathered during the study period, HPV16/18 has been almost eliminated among vaccinated women in Denmark: prevalence of these two types in the samples decreased to < 1% in 2021 from 15–17% before vaccination of girls. In addition, prevalence of the types 16/18 in women who had not been vaccinated against HPV remained at 5% which, according to the authors, "strongly indicates population immunity".
Despite the evidence of protection through vaccination, about one third of women screened during the study period still had HPV infection with high-risk HPV types not covered by the offered vaccines — and new infections with these types were more frequent in vaccinated than in unvaccinated women
There was a low prevalence of HPV16/18 during the 7-year study period and women who have been vaccinated against HPV as girls are expected to have a considerably lower risk of cervical cancer compared with previous generations. Therefore, the authors also assessed whether the current cervical screening strategies in the country could be adjusted accordingly or even stopped entirely.
The study results showed a remaining high prevalence of high-risk HPV infections in women that are not covered by the HPV vaccines and that had been detected both in vaccinated and unvaccinated women during the study period. At the same time, the authors noted a significantly higher incidence of non-vaccine high-risk HPV types among vaccinated women than in unvaccinated women.
Based on this, Nonboe et al. thus conclude that "less intensive screening seems reasonable until women vaccinated as girls with the 9-valent vaccine reach screening age, at which point screening should be reconsidered."
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