Invited commentary: multiple human papillomavirus infections and type replacement-anticipating the future after human papillomavirus vaccination

Trend of HPV 16/18 Genotypes in Cervical Intraepithelial Neoplasia Grade 3: Data for 2007-2018

Aim

In the post-vaccination era, the starting age and time intervals of cervical screening could change (older age and longer screening intervals). This scenario may be achieved by significantly reducing human papillomavirus (HPV) 16/18 prevalence (genotypes included in the current vaccines). In this regard, assessing the trend over time of these HPV infections in high-grade cervical lesions can provide information on the objective. The present study aimed to evaluate the trend of HPV 16/18 over the years 2007–2018 in women with cervical intraepithelial neoplasia (CIN) grade 3.

Methods

This is a retrospective multi-institutional study including HPV genotyped and unvaccinated women under 30 with CIN3. The sample was divided into the following periods: 2007–2010, 2011–2014, 2015–2018. HPV genotypes were grouped in genotypes 16/18, genotypes 31/33/35/52/58/67 (genetically related to HPV16), genotypes 39/45/59/68/70 (genetically related to HPV18), genotypes 31/33/45/52/58 (high-risk types included in the nonavalent vaccine), possibly carcinogenic HPV (genotypes 26/30/53/67/70/73/82/85), low-risk HPV (genotypes 6/11/40/42/43/44/54/55/61). The trend between periods and HPV genotypes was measured using the Cochran–Armitage test for trend.

Results

The final analysis included 474 participants. HPV 16/18 prevalence decreased significantly over the years (77.8% vs 68.9% vs 66.0%, respectively, Ptrend=0.027). Possibly carcinogenic HPV (genotypes 26/30/53/67/70/73/82/85) showed a significant negative prevalence trend over time (4.9% vs 1.1% vs 1.3%, respectively, Ptrend=0.046). Finally, there was a significant positive trend over the years for high-risk HPV genotypes 31/33/45/52/58 in women under 25 (9.9% vs 17.0% vs 24.0%, respectively, Ptrend=0.048).

Conclusion

The prevalence of CIN3 lesions related to HPV 16/18 genotypes decreased over time from 2007 to 2018. These data highlight a herd effect of the HPV vaccine. However, fifteen years after HPV vaccine introduction, we are still a long way from herd immunity. The increase in high-risk types 31/33/45/52/58 will need to be reassessed when the nonavalent vaccine impact will be more reliable.

Capturing multiple-type interactions into practical predictors of type replacement following human papillomavirus vaccination

Current HPV vaccines target a subset of the oncogenic human papillomavirus (HPV) types. If HPV types compete during infection, vaccination may trigger replacement by the non-targeted types. Existing approaches to assess the risk of type replacement have focused on detecting competitive interactions between pairs of vaccine and non-vaccine types. However, methods to translate any inferred pairwise interactions into predictors of replacement have been lacking. In this paper, we develop practical predictors of type replacement in a multi-type setting, readily estimable from pre-vaccination longitudinal or cross-sectional prevalence data. The predictors we propose for replacement by individual non-targeted types take the form of weighted cross-hazard ratios of acquisition versus clearance, or aggregate odds ratios of coinfection with the vaccine types. We elucidate how the hazard-based predictors incorporate potentially heterogeneous direct and indirect type interactions by appropriately weighting type-specific hazards and show when they are equivalent to the odds-based predictors. Additionally, pooling type-specific predictors proves to be useful for predicting increase in the overall non-vaccine-type prevalence. Using simulations, we demonstrate good performance of the predictors under different interaction structures. We discuss potential applications and limitations of the proposed methodology in predicting type replacement, as compared to existing approaches. This article is part of the theme issue 'Silent cancer agents: multi-disciplinary modelling of human DNA oncoviruses'.

Non-Vaccine-Type Human Papillomavirus Prevalence After Vaccine Introduction: No Evidence for Type Replacement but Evidence for Cross-Protection

BACKGROUND

We examined non-vaccine-type human papillomavirus (HPV) prevalence in a community before and during the first 8 years after vaccine introduction, to assess for (1) type replacement with any non-vaccine-type HPV and (2) cross-protection with non-vaccine types genetically related to vaccine-type HPV.

METHODS

Sexually experienced 13- to- 26-year-old women were recruited for 3 cross-sectional studies from 2006 to 2014 (N = 1180). Outcome variables were as follows: (1) prevalence of at least 1 of 32 anogenital non-vaccine-type HPVs and (2) prevalence of at least 1 HPV type genetically related to HPV-16 and HPV-18. We determined changes in proportions of non-vaccine-type HPV prevalence across the study waves using logistic regression with propensity score inverse probability weighting.

RESULTS

Vaccine initiation rates increased from 0% to 71.3%. Logistic regression demonstrated that from 2006 to 2014, there was no increase in non-vaccine-type HPV among vaccinated women (adjusted odds ratio [AOR], 1.02; 95% confidence interval [CI], 0.73-1.42), but an increase among unvaccinated women (AOR, 1.88; 95% CI, 1.16-3.04). Conversely, there was a decrease in types genetically related to HPV-16 among vaccinated (AOR, 0.57; 95% CI, 0.38-0.88) but not unvaccinated women (AOR, 1.33; 95% CI, 0.81-2.17).

CONCLUSIONS

We did not find evidence of type replacement, but did find evidence of cross-protection against types genetically related to HPV-16. These findings have implications for cost-effectiveness analyses, which may impact vaccine-related policies, and provide information to assess the differential risk for cervical cancer in unvaccinated and vaccinated women, which may influence clinical screening recommendations. The findings also have implications for public health programs, such as health messaging for adolescents, parents, and clinicians about HPV vaccination.

Evidence for cross-protection but not type-replacement over the 11 years after human papillomavirus vaccine introduction

Examination of cross-protection and type replacement after human papillomavirus (HPV) vaccine introduction is essential to guide vaccination recommendations and policies. The aims of this study were to examine trends in non-vaccine-type HPV: 1) genetically related to vaccine types (to assess for cross-protection) and 2) genetically unrelated to vaccine types (to assess for type replacement), among young women 13-26 years of age during the 11 years after HPV vaccine introduction. Participants were recruited from a hospital-based teen health center and a community health department for four cross-sectional surveillance studies between 2006 and 2017. Participants completed a survey that assessed sociodemographic characteristics and behaviors, and cervicovaginal swabs were collected and tested for 36 HPV genotypes. We determined changes in proportions of non-vaccine-type HPV prevalence and conducted logistic regression to determine the odds of infection across the surveillance studies, propensity-score adjusted to control for selection bias. Analyses were stratified by vaccination status. Among vaccinated women who received only the 4-valent vaccine (n = 1,540), the adjusted prevalence of HPV types genetically related to HPV16 decreased significantly by 45.8% (adjusted odds ratio [AOR] = 0.48, 95% confidence interval [CI] = 0.31-0.74) from 2006-2017, demonstrating evidence of cross-protection. The adjusted prevalence of HPV types genetically related to HPV18 did not change significantly (14.2% decrease, AOR = 0.83, 95% CI = 0.56-1.21). The adjusted prevalence of HPV types genetically unrelated to vaccine types did not change significantly (4.2% increase, AOR = 1.09, CI = 0.80-1.48), demonstrating no evidence of type replacement. Further studies are needed to monitor for cross-protection and possible type replacement after introduction of the 9-valent HPV vaccine.

Population-Level Effects of Human Papillomavirus Vaccination Programs on Infections with Nonvaccine Genotypes

We analyzed human papillomavirus (HPV) prevalences during prevaccination and postvaccination periods to consider possible changes in nonvaccine HPV genotypes after introduction of vaccines that confer protection against 2 high-risk types, HPV16 and HPV18. Our meta-analysis included 9 studies with data for 13,886 girls and women ≤19 years of age and 23,340 women 20-24 years of age. We found evidence of cross-protection for HPV31 among the younger age group after vaccine introduction but little evidence for reductions of HPV33 and HPV45. For the group this same age group, we also found slight increases in 2 nonvaccine high-risk HPV types (HPV39 and HPV52) and in 2 possible high-risk types (HPV53 and HPV73). However, results between age groups and vaccines used were inconsistent, and the increases had possible alternative explanations; consequently, these data provided no clear evidence for type replacement. Continued monitoring of these HPV genotypes is important.

Human Papillomavirus Prevalence and Herd Immunity after Introduction of Vaccination Program, Scotland, 2009-2013

Prevalence was reduced, and early evidence indicates herd immunity.

In 2008, a national human papillomavirus (HPV) immunization program using a bivalent vaccine against HPV types 16 and 18 was implemented in Scotland along with a national surveillance program designed to determine the longitudinal effects of vaccination on HPV infection at the population level. Each year during 2009–2013, the surveillance program conducted HPV testing on a proportion of liquid-based cytology samples from women undergoing their first cervical screening test for precancerous cervical disease. By linking vaccination, cervical screening, and HPV testing data, over the study period we found a decline in HPV types 16 and 18, significant decreases in HPV types 31, 33, and 45 (suggesting cross-protection), and a nonsignificant increase in HPV 51. In addition, among nonvaccinated women, HPV types 16 and 18 infections were significantly lower in 2013 than in 2009. Our results preliminarily indicate herd immunity and sustained effectiveness of the bivalent vaccine on virologic outcomes at the population level.

Shift in prevalence of HPV types in cervical cytology specimens in the era of HPV vaccination

The aim of the present population-based cohort study was to analyze the association between the prevalence of 32 types of human papilloma virus (HPV) in 615 female patients with abnormal cervical cytopathology findings. In total, 32 HPV types were screened by DNA array technology. HPV infection was detected in 470 women (76.42%), 419 of whom (89.15%) were infected with ≥1 high-risk (HR)-HPV type. HPV16, which is recognized as the main HR-HPV type responsible for the development of cervical cancer, was observed in 32.98% of HPV⁺ participants, followed by HPV42 (18.09%), HPV31 (17.66%), HPV51 (13.83%), HPV56 (10.00%), HPV53 (8.72%) and HPV66 (8.72%). The prevalence of HR-HPV types, which may be suppressed directly (in the case of HPV16 and 18), or possibly via cross-protection (in the case of HPV31) following vaccination, was considerably lower in participants ≤22 years of age (HPV16, 28.57%; HPV18, 2.04%; HPV31, 6.12%), compared with participants 23-29 years of age (HPV16, 45.71%; HPV18, 7.86%; HPV31, 22.86%), who were less likely to be vaccinated. Consequently, the present study hypothesizes that there may be a continuous shift in the prevalence of HPV types as a result of vaccination. Furthermore, the percentage of non-vaccine HR-HPV types was higher than expected, considering that eight HPV types formerly classified as 'low-risk' or 'probably high-risk' are in fact HR-HPV types. Therefore, it may be important to monitor non-vaccine HPV types in future studies, and an investigation concerning several HR-HPV types as risk factors for the development of cervical cancer is required.

National- and state-level impact and cost-effectiveness of nonavalent HPV vaccination in the United States

Every year in the United States more than 12,000 women are diagnosed with cervical cancer, a disease principally caused by human papillomavirus (HPV). Bivalent and quadrivalent HPV vaccines protect against 66% of HPV-associated cervical cancers, and a new nonavalent vaccine protects against an additional 15% of cervical cancers. However, vaccination policy varies across states, and migration between states interdependently dilutes state-specific vaccination policies. To quantify the economic and epidemiological impacts of switching to the nonavalent vaccine both for individual states and for the nation as a whole, we developed a model of HPV transmission and cervical cancer incidence that incorporates state-specific demographic dynamics, sexual behavior, and migratory patterns. At the national level, the nonavalent vaccine was shown to be cost-effective compared with the bivalent and quadrivalent vaccines at any coverage despite the greater per-dose cost of the new vaccine. Furthermore, the nonavalent vaccine remains cost-effective with up to an additional 40% coverage of the adolescent population, representing 80% of girls and 62% of boys. We find that expansion of coverage would have the greatest health impact in states with the lowest coverage because of the decreasing marginal returns of herd immunity. Our results show that if policies promoting nonavalent vaccine implementation and expansion of coverage are coordinated across multiple states, all states benefit both in health and in economic terms.