Examining the impact of HPV vaccination

A recent meta-analysis, published in The Lancet, examined how human papillomavirus (HPV) vaccination programs have impacted rates of HPV-related diagnoses in the little more than 10 years since vaccination was implemented. Sixty million individuals were included in the review and the 8 years of post-vaccination follow-up data indicate that vaccination has had a substantial impact on reducing HPV infection, CIN2+, and anogenital warts.  

For the systematic review, the authors searched MEDLINE and Embase for studies published between February 1, 2014 and October 11, 2018. Eligible studies compared the frequency (prevalence or incidence) of at least one HPV-related endpoint, including genital HPV infection, anogenital wart diagnoses or cervical intraepithelial neoplasia grade 2+ (CIN2+), between pre-vaccination and post-vaccination periods. The studies also had to use the same population sources and recruitment methods before and after vaccination. All analyses were stratified by sex, age, and years since vaccine introduction.

The authors identified 1702 articles that were potentially eligible. Sixty-five articles from 14 high-income countries were included in the final review (23 for HPV infection, 29 for anogenital warts and 13 for CIN2+). 

Five to 8 years of vaccination, prevalence of HPV 16 and 18 decreased significantly by 83% (relative risk [RR] 0.17; 95% CI 0.11 – 0.25) among girls between ages 13 and 19. Among women aged 20 to 24, prevalence decreased by 66% (RR 0.34; 95% CI 0.23 – 0.49). Although not as significant as HPV 16 and 18, prevalence of HPV 31, 33, and 45 decreased significantly by 54% (RR 0.46; 95% CI 0.33 – 0.66) among girls aged 13 to 19. Among women aged 20 to 24, the decrease was not significant. 

Anogenital wart diagnoses significantly decreased among girls and women aged 15 to 19, 20 to 24, and 25 to 29 in the first 4 years following implementation. Diagnoses 5 to 8 years after implementation also decreased by 67% (RR 0.33; 95% CI 0.24 – 0.46) among girls aged 15 to 19, by 54% (RR 0.46; 95% CI 0.36 – 0.60) among women aged 20 to 24, and by 31% (RR 0.69; 95% CI 0.47 – 0.98) among women aged 25 to 29. 

At 5 to 9 years after implementation of vaccination, rates of CIN2+ decreased significantly by 51% (RR 0.49; 95% CI 0.42 – 0.58) among girls aged 15 to 19 and among women aged 20 to 24, this number decreased by 31% (RR 0.69; 95% CI 0.57 – 0.84). Among mostly unvaccinated women, CIN2+ significantly increased in women between ages 25 to 29 and 30 to 39, respectively (19% [RR 1.19, 95% CI 1.06 – 1.32] and 23% [RR 1.23; 95% CI 1.13 – 1.34].

The authors believe the results of the meta-analysis reinforce the recently revised position of the World Health Organization to recommend HPV vaccination to multiple age cohorts of girls with the hope that cervical cancer can be eliminated if proper population-level vaccination coverage can be achieved.