Vaccination With Moderate Coverage Eradicates Oncogenic Human Papillomaviruses If a Gender-Neutral Strategy Is Applied.

BACKGROUND: Human papillomavirus (HPV) vaccination of girls with very high (>90%) coverage has the potential to eradicate oncogenic HPVs, but such high coverage is hard to achieve. However, the herd effect (HE) depends both on the HPV type and the vaccination strategy. METHODS: We randomized 33 Finnish communities into gender-neutral HPV16/18 vaccination, girls-only HPV16/18 vaccination, and hepatitis B virus vaccination arms. In 2007-2010, 11 662 of 20 513 of 40 852 of 39 420 resident boys/girls from 1992 to 1995 birth cohorts consented. In 2010-2014, cervicovaginal samples from vaccinated and unvaccinated girls at age 18.5 years were typed for HPV6/11/16/18/31/33/35/39/45/51/52/56/58/59/66/68. Vaccine efficacy for vaccinated girls, HE for unvaccinated girls, and the protective effectiveness (PE) for all girls were estimated. We extended the community-randomized trial results about vaccination strategy with mathematical modeling to assess HPV eradication. RESULTS: The HE and PE estimates in the 1995 birth cohort for HPV18/31/33 were significant in the gender-neutral arm and 150% and 40% stronger than in the girls-only arm. Concordantly, HPV18/31/33 eradication was already predicted in adolescents/young adults in 20 years with 75% coverage of gender-neutral vaccination. With the 75% coverage, eventual HPV16 eradication was also predicted, but only with the gender-neutral strategy. CONCLUSIONS: Gender-neutral vaccination is superior for eradication of oncogenic HPVs.

Human Papillomavirus Prevalence in Unvaccinated Heterosexual Men After a National Female Vaccination Program.

Background: In Australia, high uptake of the quadrivalent human papillomavirus (4vHPV) vaccine has led to reductions in the prevalence of human papillomavirus (HPV) genotypes 6, 11, 16, and 18 in women and girls aged ≤25 years. We evaluated the impact of the program impact on HPV prevalence in unvaccinated male subjects. Methods: Sexually active heterosexual male subjects aged 16-35 years were recruited in 2014-2016. Participants provided a self-collected penile swab sample for HPV genotyping (Roche Linear Array) and completed a demographic and risk factor questionnaire. Results: The prevalence of 4vHPV genotypes among 511 unvaccinated male subjects was significantly lower in those aged ≤25 than in those aged >25 years: 3.1% (95% confidence interval, 1.5%-5.7%) versus 13.7% (8.9%-20.1%), respectively (P < .001); adjusted prevalence ratio, 0.22 (.09-.51; P < .001). By contrast, the prevalence of high-risk HPV genotypes other than 16 and 18 remained the same across age groups: 16.8% (95% confidence interval, 12.6%-21.9%) in men aged ≤25 years and 17.9% (12.4%-25.0%) in those aged >25 years (P = .76); adjusted prevalence ratio, 0.98, (.57-1.37; P = .58). Conclusions: A 78% lower prevalence of 4vHPV genotypes was observed among younger male subjects. These data suggest that unvaccinated men may have benefited from herd protection as much as women from a female-only HPV vaccination program with high coverage.

Modelling the Public Health Impact of MenACWY and MenC Adolescent Vaccination Strategies in Germany.

INTRODUCTION: Invasive meningococcal disease (IMD) causes significant mortality and long-term sequelae. This study assesses the potential public health impact of adolescent vaccination strategies employing MenACWY and MenC vaccines in Germany, where the existing meningococcal immunisation programme predominantly involves MenC administration in toddlers. METHODS: A dynamic transmission model was developed to simulate the carriage of five meningococcal serogroup compartments (AY/B/C/W/Other) from 2019 until 2060 within 1-year age groups from 0 to 99 years of age. IMD cases were estimated based on case-carrier ratios. The model considered vaccine effectiveness against carriage acquisition and IMD. RESULTS: The model predicts that introducing MenACWY adolescent vaccination could lead to a considerable reduction in IMD incidence, with the potential to prevent up to 65 cases per year and a cumulative total of 1467 cases by 2060. This decrease, mainly driven by herd effects, would result in a reduction of IMD incidence across all age groups, regardless of vaccination age. Furthermore, implementing MenACWY vaccination in adolescents is projected to decrease annual MenACWY-related IMD mortality by up to 64%, equating to an overall prevention of 156 IMD deaths by 2060. These protective outcomes are expected to culminate in approximately 2250 life years gained (LYG) throughout the model's projected time horizon. In contrast, the adoption of MenC vaccination in adolescents is predicted to have minimal influence on both IMD incidence and mortality, as well as on LYG. CONCLUSION: The results of this study demonstrate that implementing MenACWY vaccination for adolescents in Germany is likely to notably reduce IMD incidence and mortality across age groups. However, the introduction of MenC adolescent vaccination shows only limited impact. Considering the extensive healthcare resources typically required for IMD management, these findings suggest the potential for economic benefits associated with the adoption of MenACWY adolescent vaccination, warranting further cost-effectiveness analysis.

Assessing Vaccine Herd Protection by Killed Whole-Cell Oral Cholera Vaccines Using Different Study Designs.

The population level effectiveness of a vaccine may arise as the result of direct protection of vaccinees and vaccine herd protection, which may protect non-vaccinees, vaccinees, or both. Indirect, total, enhanced, and overall vaccine protection are measures of vaccine herd protection. The level of population level effectiveness induced by a vaccine is driven by several factors, including known vaccine-induced protective efficacy, the magnitude, and distribution of vaccine coverage at a point in time and the extent to which different groups mix with one another in the community. Data on vaccine herd protection are valuable in understanding the importance and cost-effectiveness in deploying the e vaccine in public health program. Killed whole-cell (WC) oral cholera vaccines (OCVs) have been evaluated for herd protection in various study settings, leveraging geographic information system (GIS) tools for the analyses. This article provides a brief description of the herd protective effects of killed WC OCVs measured using various study deigns that include (a) individually randomized, controlled clinical trials, (b) cluster randomized clinical trials, (c) observational cohort studies, and (d) observational case-control studies. In all of the study designs, significant herd protection was observed in unvaccinated persons as well as in the community as a whole. The findings of these studies suggest that using killed WC OCV as a public health tool for controlling cholera is impactful and cost-effective.

Implications and measurement of herd protection (indirect effects) for enteric vaccine development.

Diarrhea remains one of the top five causes of disease and death among young children in developing nations. Fortunately, scientists are making progress developing vaccines against enterotoxigenic E. coli (ETEC) and Shigella, two of the leading diarrhea pathogens. As vaccine developers start to consider field efficacy trials of these vaccines, they should be aware of the importance of evaluating not only vaccine direct effects on the immunized, but also the herd effects that vaccination can afford to the unimmunized in a community. In a workshop held at the conference titled "Vaccines against Shigella and ETEC (VASE)", we described to participants what herd effects are and we presented on methods used in cholera and rotavirus studies that could be useful for future ETEC and Shigella vaccine trials conducted in low and middle-income nations. We also presented evidence on the effects of vaccine herd effects for estimates of vaccine cost-effectiveness.

Declines in HPV vaccine type prevalence in women screened for cervical cancer in the United States: Evidence of direct and herd effects of vaccination.

BACKGROUND: Human papillomavirus (HPV) vaccine has been recommended in the United States since 2006 for routine vaccination of girls at age 11-12 years and through age 26 years for women not previously vaccinated. Changes in vaccine-type HPV (VT) prevalence can be used to evaluate vaccine impact, including herd effects. METHODS: We determined type-specific HPV in cytology specimens from women aged 20-29 years screened for cervical cancer at Kaiser Permanente Northwest in 2007 and in two vaccine era periods: 2012-2013 and 2015-2016. Detection and typing used L1 consensus PCR with hybridization for 37 types, including quadrivalent vaccine types (HPV 6/11/16/18). RESULTS: Among 20-24 year-olds in 2012-2013 and 2015-2016, 44% and 64% had a history of ≥1-dose vaccination. VT prevalence decreased from 13.1% in 2007 to 2.9% in 2015-2016 (prevalence ratio [PR] = 0.22; 95% confidence interval [CI] 0.17-0.29). HPV 31 prevalence was also lower in the vaccine periods compared with 2007. VT prevalence in 2015-2016 among 20-24 year-olds was lower in both vaccinated, 1.3% (PR = 0.10; 95% CI 0.06-0.16), and unvaccinated women, 5.8% (PR = 0.45; 95% CI 0.33-0.61). Among 25-29 year-olds, 21% and 32% had a history of ≥1-dose vaccination. VT prevalence decreased from 8.1% in 2007 to 5.0% in 2015-2016 (PR = 0.62; 95% CI 0.50-0.78). Non-VT high risk prevalence was higher in the vaccine periods compared with the pre-vaccine era in both age groups, however, not in 2015-2016 compared with 2012-2013. CONCLUSION: Within 9-10 years of vaccine introduction, VT prevalence decreased 78% among 20-24 year-olds and 38% in 25-29 year-olds. There were declines in both vaccinated and unvaccinated women, showing evidence of direct and herd protection.

Human papillomavirus vaccination and the role of herd effects in future cancer control planning: a review.

INTRODUCTION: Vaccine herd effects are the indirect protection that vaccinated persons provide to those who remain susceptible to infection, due to the reduced transmission of infections. Herd effects have been an important part of the discourse on how to best implement human papillomavirus (HPV) vaccines and prevent HPV-related diseases. AREAS COVERED: In this paper, we review the theory of HPV vaccine herd effects derived from mathematical models, give an account of observed HPV vaccine herd effects worldwide, and examine the implications of vaccine herd effects for future cervical cancer screening efforts. EXPERT COMMENTARY: HPV vaccine herd effects improve the cost-effectiveness of vaccinating preadolescent girls, but contribute to making gender-neutral vaccination less economically efficient. Vaccination coverage and sexual mixing patterns by age are strong determinants of herd effects. Many countries worldwide are starting to observe reductions in HPV-related outcomes likely attributable to herd effects, most notably declining anogenital warts in young men, and declining HPV-16/18 infection prevalence in young unvaccinated women. Policy makers making recommendations for cervical cancer screening will have to consider HPV vaccination coverage and herd effects, as these will affect the positive predictive value of screening and the risk of cervical cancer in unvaccinated women.

Generalized herd effects and vaccine evaluation: impact of live influenza vaccine on off-target bacterial colonisation.

Interactions between pathogens and commensal microbes are major contributors to health and disease. Infectious diseases however are most often considered independent, viewed within a one-host one-pathogen paradigm and, by extension, the interventions used to treat and prevent them are measured and evaluated within this same paradigm. Vaccines, especially live vaccines, by stimulating immune responses or directly interacting with other microbes can alter the environment in which they act, with effects that span across pathogen species. Live attenuated infl uenza vaccines for example, while safe, increase upper respiratory tract bacterial carriage density of important human commensal pathogens like Streptococcus pneumoniae and Staphylococcus aureus. Further, by altering the ecological niche and dynamics of phylogenetically distinct microbes within the host, vaccines may unintentionally affect transmission of non-vaccine targeted pathogens. Thus, vaccine effects may span across species and across scales, from the individual to the population level. In keeping with traditional vaccine herd-effects that indirectly protect even unvaccinated individuals by reducing population prevalence of vaccine-targeted pathogens, we call these cross-species cross-scale effects "generalized herd-effects". As opposed to traditional herd-effects, "generalized" relaxes the assumption that the effect occurs at the level of the vaccine-target pathogen and "herd effect" implies, as usual, that the effects indirectly impact the population at large, including unvaccinated bystanders. Unlike traditional herd-effects that decrease population prevalence of the vaccine-target, generalized herd-effects may decrease or increase prevalence and disease by the off-target pathogen. LAIV, for example, by increasing pneumococcal density in the upper respiratory tract of vaccine recipients, especially children, may increase pneumococcal transmission and prevalence, leading to excess pneumococcal invasive disease in the population, especially among the elderly and others most susceptible to pneumococcal disease. However, these effects may also be beneficial, for example the large reductions in all-cause mortality noted following measles vaccines. Here we discuss evidence for these novel vaccine effects and suggest that vaccine monitoring and evaluation programs should consider generalized herd effects to appreciate the full impacts of vaccines, beneficial or detrimental, across species and scales that are inevitably hiding in plain sight, affecting human health and disease.

Spillover effects on health outcomes in low- and middle-income countries: a systematic review.

Background: Many interventions delivered to improve health may benefit not only direct recipients but also people in close physical or social proximity. Our objective was to review all published literature about the spillover effects of interventions on health outcomes in low-middle income countries and to identify methods used in estimating these effects. Methods: We searched 19 electronic databases for articles published before 2014 and hand-searched titles from 2010 to 2013 in five relevant journals. We adapted the Cochrane Collaboration's quality grading tool for spillover estimation and rated the quality of evidence. Results: A total of 54 studies met inclusion criteria. We found a wide range of terminology used to describe spillovers, a lack of standardization among spillover methods and poor reporting of spillovers in many studies. We identified three primary mechanisms of spillovers: reduced disease transmission, social proximity and substitution of resources within households. We found the strongest evidence for spillovers through reduced disease transmission, particularly vaccines and mass drug administration. In general, the proportion of a population receiving an intervention was associated with improved health. Most studies were of moderate or low quality. We found evidence of publication bias for certain spillover estimates but not for total or direct effects. To facilitate improved reporting and standardization in future studies, we developed a reporting checklist adapted from the CONSORT framework specific to reporting spillover effects. Conclusions: We found the strongest evidence for spillovers from vaccines and mass drug administration to control infectious disease. There was little high quality evidence of spillovers for other interventions.

Herd effects of child vaccination with pneumococcal conjugate vaccine against pneumococcal non-invasive community-acquired pneumonia: What is the evidence?

Quantification of pneumococcal conjugate vaccines (PCVs) herd effects are mainly performed on invasive pneumococcal disease (IPD) but there is conflicting evidence regarding herd effects of PCVs on non-IPD pneumococcal community-acquired pneumonia. This review summarizes the available literature on herd effects of PCVs on non-IPD pneumococcal community-acquired pneumonia.

Measuring indirect effects of rotavirus vaccine in low income countries.

Widespread introduction of rotavirus vaccines has led to major reductions in the burden of rotavirus gastroenteritis worldwide. Vaccine effectiveness is diminished, however, in low income countries, that harbour the greatest burden of rotavirus attributed morbidity and mortality. Indirect effects of rotavirus vaccine (herd immunity and herd protection) could increase population level impact and improve vaccine cost effectiveness in such settings. While rotavirus vaccine indirect effects have been demonstrated in high and middle income countries, there are very little data from low income countries where force of infection, population structures and vaccine schedules differ. Targeted efforts to evaluate indirect effects of rotavirus vaccine in low income countries are required to understand the total impact of rotavirus vaccine on the global burden of rotavirus disease.