The near disappearance of genital warts in young women four years after commencing a national human papillomavirus (HPV) vaccination programme
Read TRH, Hocking JS, Chen MY et al (2011) 87; 544-547
This was a retrospective, single-centre, cohort study, of the trends in genital warts (GWs) at Melbourne Sexual Health Centre in Australia from July 2004 up to the end of June 2011. This was adjusted for sexual risk determined by the number of sexual partners based on an HPV vaccination policy that was started in April 2007 and aimed at women less than 27 years of age. It was a pre-requisite that those included in the study were either Australian citizens, permanent residents, or those who had arrived within three years of presentation to the clinic as this latter group was not eligible for the HPV vaccination programme. It was however, not mentioned how the data was actually captured from the database or how it was adjusted for the number of sexual partners.
During the seven-year period, a total of 52,454 new patients were seen at the sexual health clinic and 5,021 clients were diagnosed with GWs giving a prevalence of 9.6%. The results of the prevalence and their adjusted odds ratio and confidence intervals were displayed on a table. This showed that the largest decline occurred in the period between 2007/2008 and 2010/2011 in women under 21 years of age (from 18.6 to 1.9%) and in heterosexual men of the same age (from 22.9% to 2.9%). There was also a significant decline in GWs diagnosis in women between 22 and 29 years, but not older women or older heterosexual men. However, before July 2007, GW diagnoses in women increased significantly with each year and were unchanged in all other groups.
A graphical representation of the trends in GWs diagnosis over the period is also shown, which clearly illustrates the decline in GWs in women under 21 years of age and in heterosexual men of the same age, and a continuing plateau in men who have sex with men.
The authors suggests that the significance of the results in heterosexual men and women under 21 since 2007 corresponds to the introduction of the HPV vaccine in girls and young women, owing to the fact that no reduction was seen in women over 30 years and in men who have sex with men, and non-residents since these were not eligible for the free vaccination programme. Since the data was adjusted for the number of sexual partners it was also suggested that this may add strength to the findings and provide evidence that the vaccination programme may lead to the near disappearance of genital warts from the heterosexual population. This may not be completely true, as the study fails to recognise the impact of behavioural change, health education and other measures including use of contraception, which may be contributory to this decline.
They also opined that the data provide the first evidence that a vaccination programme with 70% coverage of young women may lead to the near disappearance of GWs from the heterosexual population and suggests that the reproductive rate of HPV types six and 11 in young Australians is now below one. The less marked decline in women aged 21-29 years is put down to the possibilities that women in this age group may have already been infected with HPV type six or 11 and thus there may be a delay in appearance of genital warts after infection, which may be as late as 45 months after the primary infection, or the herd immunity may be weaker in this age group. This also suggests that a significant ‘wash out’ period may exist after HPV vaccination when lesions could emerge from an HPV infection acquired after vaccination. The data also indicates that MSM, whose rate of anal cancer is at least as high as cervical cancer in women, are receiving no benefit from the current HPV vaccination programme.
The authors admit quite rightly there are quite a few limitations to consider in the interpretation and the generalisations of these data. The data are compiled from a single sexual health centre and may not be representative of what happens in the whole of Australia. The other consideration is that this was a retrospective study, making it very difficult to control for confounding factors. The study does, however, highlight the urgent need to address the issue of continuing transmission of genital warts amongst men who have sex with men.