Population-level impact and herd effects following the introduction of human papillomavirus vaccination programmes: updated systematic review and meta-analysis

Abstract

Background: More than 10 years have elapsed since human papillomavirus (HPV) vaccination was implemented. We did a systematic review and meta-analysis of the population-level impact of vaccinating girls and women against human papillomavirus on HPV infections, anogenital wart diagnoses, and cervical intraepithelial neoplasia grade 2+ (CIN2+) to summarise the most recent evidence about the effectiveness of HPV vaccines in real-world settings and to quantify the impact of multiple age-cohort vaccination.

Methods: In this updated systematic review and meta-analysis, we used the same search strategy as in our previous paper. We searched MEDLINE and Embase for studies published between Feb 1, 2014, and Oct 11, 2018. Studies were eligible if they compared the frequency (prevalence or incidence) of at least one HPV-related endpoint (genital HPV infections, anogenital wart diagnoses, or histologically confirmed CIN2+) between pre-vaccination and post-vaccination periods among the general population and if they used the same population sources and recruitment methods before and after vaccination. Our primary assessment was the relative risk (RR) comparing the frequency (prevalence or incidence) of HPV-related endpoints between the pre-vaccination and post-vaccination periods. We stratified all analyses by sex, age, and years since introduction of HPV vaccination. We used random-effects models to estimate pooled relative risks.

Findings: We identified 1702 potentially eligible articles for this systematic review and meta-analysis, and included 65 articles in 14 high-income countries: 23 for HPV infection, 29 for anogenital warts, and 13 for CIN2+. After 5-8 years of vaccination, the prevalence of HPV 16 and 18 decreased significantly by 83% (RR 0·17, 95% CI 0·11-0·25) among girls aged 13-19 years, and decreased significantly by 66% (RR 0·34, 95% CI 0·23-0·49) among women aged 20-24 years. The prevalence of HPV 31, 33, and 45 decreased significantly by 54% (RR 0·46, 95% CI 0·33-0·66) among girls aged 13-19 years. Anogenital wart diagnoses decreased significantly by 67% (RR 0·33, 95% CI 0·24-0·46) among girls aged 15-19 years, decreased significantly by 54% (RR 0·46, 95% CI 0.36-0.60) among women aged 20-24 years, and decreased significantly by 31% (RR 0·69, 95% CI 0·53-0·89) among women aged 25-29 years. Among boys aged 15-19 years anogenital wart diagnoses decreased significantly by 48% (RR 0·52, 95% CI 0·37-0·75) and among men aged 20-24 years they decreased significantly by 32% (RR 0·68, 95% CI 0·47-0·98). After 5-9 years of vaccination, CIN2+ decreased significantly by 51% (RR 0·49, 95% CI 0·42-0·58) among screened girls aged 15-19 years and decreased significantly by 31% (RR 0·69, 95% CI 0·57-0·84) among women aged 20-24 years.

Interpretation: This updated systematic review and meta-analysis includes data from 60 million individuals and up to 8 years of post-vaccination follow-up. Our results show compelling evidence of the substantial impact of HPV vaccination programmes on HPV infections and CIN2+ among girls and women, and on anogenital warts diagnoses among girls, women, boys, and men. Additionally, programmes with multi-cohort vaccination and high vaccination coverage had a greater direct impact and herd effects.

Funding: WHO, Canadian Institutes of Health Research, Fonds de recherche du Québec - Santé.

Figure 1:. Study selection

Two articles on anogenital warts from our previous systematic review and meta-analysis were not included in this update: Sandø and colleagues and Nsouli-Maktabi and colleagues. Sandø and colleagues was one of two studies we had previously found that analysed the entire Danish population for the same period, but we included the study by Baandrup and colleagues in our current analysis because they updated their data and had a longer follow-up. We excluded the study by Nsouli-Maktabi and colleagues because it was done among members of the US armed forces and not in the general population. NHANES=National Health and Nutrition Examination Survey.

Figure 2:. Changes in the prevalence of HPV infections between pre-vaccination and post-vaccination periods

HPV=human papillomavirus. *p values are associated with the χ² statistic.

Figure 3:. Changes in anogenital wart diagnoses between pre-vaccination and post-vaccination periods in countries using the quadrivalent vaccine

*p values are associated with the χ² statistic.

Figure 4:. Changes in anogenital wart diagnoses during the 8 years after the introduction of girls-only human papillomavirus vaccination in countries using the quadrivalent vaccine

We stratified by number of cohorts vaccinated and routine vaccination coverage. Countries with single-cohort vaccination and/or low coverage (in red) were Canada (Ontario, Manitoba^,) and Italy with single-cohort vaccination and high coverage; and Germany,^, Belgium, Sweden,^, and the USA^,, with multi-cohort vaccination and low coverage. Countries with multi-cohort vaccination and high coverage (in blue) were Australia,^,,,, Denmark,^, New Zealand,^, and Canada (Quebec).

Figure 5:. Changes in CIN2+ among screened girls and women between the pre-vaccination and post-vaccination periods

CIN2+=cervical intraepithelial neoplasia grade 2+. *p values are associated with the χ² statistic.

Figure 6:. Changes in CIN2+ among screened girls and women during the first 7 years after the introduction of girls-only human papillomavirus vaccination, in countries with multi-cohort vaccination and high vaccination coverage

Countries with multi-cohort vaccination and high coverage (≥50%) were Australia,^, Canada (British Columbia), Denmark, Scotland, and the USA.^,,, For CIN2+ analysis, the USA was categorised as a country with multi-cohort vaccination and high routine vaccination coverage because several US data indicate an association between screening participation and human papillomavirus vaccination.^,,, Thus, the vaccination coverage among screened girls and women is likely to be higher than the overall vaccination coverage in the population. We did a sensitivity analysis excluding the USA from countries with multi-cohort and high vaccination coverage and results were unchanged. CIN2+=cervical intraepithelial neoplasia grade 2+.