The introduction of the human papillomavirus according to a meta-analysis of data from more than 60 million individuals worldwide.
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Mélanie Drolet, PhD, from the Centre de recherche du CHU de Québec–Université Laval, and coauthors of the HPV Vaccination Impact Study Group reported the results of a systematic review and meta-analysis of 65 studies showing pre- and postvaccination frequency of at least one HPV-related endpoint published in the Lancet. The studies were conducted in 14 high-income countries, 12 of which were vaccinating only women and girls, with the results at 5-8 years published in the Lancet.
At 5-8 years after a vaccination program was implemented, there was a significant 83% reduction in the prevalence of HPV 16 and 18, both of which are targeted by the vaccine, among girls aged 13-19 years; a 66% reduction among women aged 20-24 years; and a 37% reduction in women aged 25-29 years, even though most of these women were unvaccinated.
There also were significant decreases at 5-8 years in the prevalence of HPV subtypes 31, 33, and 45, which are not included in the vaccine but against which the vaccine appears to offer cross-protection. Among girls aged 13-19 years, there was a significant 54% reduction in the prevalence of these subtypes, among women aged 20-24 years there was a nonsignificant 28% decrease, but among women aged 25-29 years, there was no significant decrease.
The analysis also found significant declines in the prevalence of cervical intraepithelial neoplasias (CINs) of grade 2 or above. At 5-9 years after vaccination was introduced, CIN2+ decreased by 51% among girls aged 15-19 years who also were screened for cervical cancer, and by 31% among women aged 20-24 years.
However, over the same time period, the rates of CIN2+ increased by a significant 19% among mostly unvaccinated women aged 25-29 years and 23% among mostly unvaccinated women aged 30-39 years, despite both groups being screened for cervical abnormalities.
While most of the countries in the study vaccinated only girls and women, two studies did find nonsignificant decreases in the prevalence of HPV 16, 18, 31, 33, and 45 among boys aged 16-19 years, but not among men aged 20-24 years.
HPV vaccination also was associated with significant declines in the incidence of anogenital warts among both males and females. In the first 4 years alone, vaccination was associated with significant reductions in anogenital wart diagnoses among females aged 15-29 years, as well as nonsignificant but “substantial” reductions in unvaccinated boys aged 15-19 years.
After 5-8 years, anogenital wart diagnoses decreased by 67% among girls aged 15-19 years, significantly by 54% among women aged 20-24 years, and 31% among women aged 25-29 years – all significant changes. Among boys aged 15-19 years, anogenital wart diagnoses decreased by a significant 48%, and among men aged 20-24 years they decreased by a significant 32%.
The decreases in anogenital wart diagnoses were even greater in countries that implemented vaccination among multiple cohorts simultaneously and achieved high vaccination coverage, compared with countries that vaccinated only one cohort at a time or had low routine vaccination coverage.
“Our study is the first to show the real-world additional benefit of multicohort HPV vaccination and high routine vaccination coverage, and the fast and substantial herd effects of vaccination in countries which implement these measures,” wrote Dr. Drolet and coauthors. “The greater impact of multicohort vaccination was similar when restricting the analyses to countries with high routine vaccination coverage.”
They pointed to the World Health Organization’s recently revised position on HPV vaccination, which now recommends vaccination of multiple cohorts of girls aged 9-14 years, although they raised the question of what might be the optimal number of age cohorts. “Number needed to vaccinate and cost-effectiveness analyses in high-income countries suggest that vaccinating multiple cohorts of individuals up to 18 years of age is highly efficient and cost effective.”
This analysis by Drolet et al. “provides compelling evidence for HPV vaccine efficacy on all outcomes explored and for almost all age strata,” Dr. Silvia de Sanjose, of PATH in Seattle, and Dr. Sinead Delany-Moretlwe of the Wits Reproductive Health and HIV Institute at the University of Witwatersrand in Johannesburg, said in an accompanying editorial (Lancet. 2019 Jun 26. doi: 10.1016/ S0140-6736[19]30549-5). This study shows just how effective HPV vaccination can be across a range of outcomes and ages, and also demonstrates the herd immunity benefits, particularly when multiple cohorts are vaccinated and there is high vaccination coverage.
One key limitation of this analysis is the lack of data from low- and middle-income countries. The data by Drolet et al. “emphasise the importance of redoubling our efforts to tackle the fiscal, supply, and programmatic barriers that currently limit HPV vaccine programmes; with these efforts, HPV vaccination could become a hallmark investment of cancer prevention in the 21st century,” Dr. de Sanjose and Dr. Delany-Moretlwe concluded.
The study was funded by WHO, Canadian Institutes of Health Research, and Fonds de recherche du Québec–Santé. No conflicts of interest were declared.
Dr. de Sanjose declared previous institutional support from Merck.
SOURCE: Drolet M et al. Lancet 2019 Jun 26. doi: 10.1016/ S0140-6736(19)30298-3.