Reduced dose human papillomavirus vaccination: An update of the current state-of-the-art

Australia's Role in Pneumococcal and Human Papillomavirus Vaccine Evaluation in Asia-Pacific

Australian researchers have made substantial contributions to the field of vaccinology over many decades. Two examples of this contribution relate to pneumococcal vaccines and the human papillomavirus (HPV) vaccine, with a focus on improving access to these vaccines in low- and lower-middle-income countries (LLMICs). Many LLMICs considering introducing one or both of these vaccines into their National Immunisation Programs face significant barriers such as cost, logistics associated with vaccine delivery. These countries also often lack the resources and expertise to undertake the necessary studies to evaluate vaccine performance. This review summarizes the role of Australia in the development and/or evaluation of pneumococcal vaccines and the HPV vaccine, including the use of alternative vaccine strategies among countries situated in the Asia-Pacific region. The outcomes of these research programs have had significant global health impacts, highlighting the importance of these vaccines in preventing pneumococcal disease as well as HPV-associated diseases.

From the Infection to the Immunotherapy in Cervical Cancer: Can We Stop the Natural Course of the Disease?

Cervical cancer (CC) is the second leading cause of cancer death in women aged 20–39 years. Persistent infection with oncogenic types of human papillomavirus (HPV) represents the most important risk factor for the development of cervical cancer. Three HPVs vaccines are currently on the global market: bivalent, quadrivalent, and nonavalent. The nonavalent vaccine provides protection against almost 90% of HPV-related CC. Despite availability of primary and secondary prevention measures, CC persists as one of the most common cancers among women around the world. Although CC is a largely preventable disease, management of persistent or recurrent CC no longer amenable to control with surgery or radiation therapy has not improved significantly with the progress of modern chemotherapy and disseminated carcinoma of the cervix remains a discouraging clinical entity with a 1-year survival rate between 10% and 15%. Over the last few years, there has been increasing interest in immunotherapy as a strategy to fight tumors. This article focuses on recent discoveries about the HPV vaccine and immunotherapies in the prevention and treatment of CC, highlighting the future view.

Efficacy and immunogenicity of a single dose of human papillomavirus vaccine compared to no vaccination or standard three and two-dose vaccination regimens: A systematic review of evidence from clinical trials

OBJECTIVES

This study aimed to systematically review the literature on the efficacy and immunogenicity of single-dose HPV vaccination compared to no vaccination or multi-dose schedules among vaccine trial participants.

METHODS

Medline, EMBASE, Global Health Database and Cochrane Central Register of Controlled Trials were searched for publications and conference abstracts (dated January 1999-August 2018) using MeSH and non-MeSH terms for human papillomavirus AND vaccines AND (immunogenicity OR efficacy/effectiveness) AND dosage. Search results were screened against pre-specified eligibility criteria. Data were extracted from included articles, and a narrative synthesis conducted on efficacy against HPV16/18 infection and humoral immunogenicity.

RESULTS

Seven of 6,523 unique records identified were included in the review. Six were nested observational studies of participants randomised to receive two or three doses in three large HPV vaccine trials, in which some participants did not complete their allocated schedules. One small pilot study prospectively allocated participants to receive one or no vaccine dose. Frequency of HPV16/18 infection was low (e.g. <1% for 12-month-persistent infection) in all vaccinated participants up to seven years post vaccination and did not significantly differ by number of doses (p > 0.05 in all cases). Frequency of infection was significantly lower in one-dose recipients compared to unvaccinated controls (p < 0.01 for all infection endpoints in each study). HPV16/18 seropositivity rates were high in all HPV vaccine recipients (100% in three of four studies reporting this endpoint), though antibody levels were lower with one compared to two or three doses.

CONCLUSIONS

This review supports the premise that one HPV vaccine dose may be as effective in preventing HPV infection as multi-dose schedules in healthy young women. However, it also highlights the paucity of available evidence from purpose-designed, prospectively-randomised trials. Results from ongoing clinical trials assessing the efficacy and immunogenicity of single-dose HPV vaccination compared to currently-recommended schedules are awaited.

Recombinant human papillomavirus nonavalent vaccine in the prevention of cancers caused by human papillomavirus

Human papillomavirus (HPV) types 16 and 18 cause 70% of cervical cancer cases globally. The nonavalent HPV vaccine (9vHPV) was licensed in 2014 and protects against the next five most common cancer-causing HPV types (HPV 31/33/45/52/58) after HPV 16/18. Phase III clinical studies have demonstrated high vaccine efficacy (>90%) against cervical, vulvar, and vaginal precancers caused by these additional types, and have shown comparable immunogenicity to the shared genotypes to quadrivalent HPV vaccine (4vHPV). Vaccine efficacy and antibody responses for 9vHPV are found to persist for at least five years while longer-term observational studies are ongoing to monitor long-term vaccine effectiveness. The implementation of 9vHPV has the potential to prevent up to 93% of cervical cancer cases, as well as a significant proportion of other HPV-related anogenital cancers. This review article summarizes the current evidence for 9vHPV in terms of vaccine efficacy against HPV infection and related anogenital precancers, safety, and immunogenicity, as well as discussing the potential impact of this vaccine on the cervical cancer burden globally.

Vaccine programme stakeholder perspectives on a hypothetical single-dose human papillomavirus (HPV) vaccine schedule in low and middle-income countries

BACKGROUND

The World Health Organization (WHO) recommends a 2-dose HPV vaccine schedule for girls aged 9-14 years. As randomised controlled trials assessing the immunogenicity and efficacy of a 1-dose schedule are ongoing, we interviewed immunisation programme managers and advisors in low and middle-income countries (LMIC) about a hypothetical, future reduction in the HPV vaccine schedule.

METHODS

We conducted semi-structured interviews with LMIC immunisation programme managers and national immunisation technical advisory group members (key informants; KIs) in 2017, recruited for their knowledge/experience in national HPV vaccine policy and provision. Data were analysed thematically.

RESULTS

We conducted 30 interviews with KIs from 18 countries. Perceived advantages of a 1-dose schedule included reduced logistical and financial resources needed for vaccine delivery, fewer cold chain requirements and easier integration into routine immunisation services. Perceived challenges included health worker hesitancy, resources needed to re-mobilise communities and re-train health workers, potential misrepresentation of schedule changes by anti-vaccine groups or the media. Half of interviewees suggested a WHO recommendation would be necessary prior to policy change.

CONCLUSIONS

We found wide-ranging support among LMIC immunisation managers and advisors for a 1-dose vaccine schedule if research demonstrated immunological and clinical evidence of efficacy, and WHO provided a formal recommendation.

Immunogenicity of HPV prophylactic vaccines: Serology assays and their use in HPV vaccine evaluation and development

When administered as standard three-dose schedules, the licensed HPV prophylactic vaccines have demonstrated extraordinary immunogenicity and efficacy. We summarize the immunogenicity of these licensed vaccines and the most commonly used serology assays, with a focus on key considerations for one-dose vaccine schedules. Although immune correlates of protection against infection are not entirely clear, both preclinical and clinical evidence point to neutralizing antibodies as the principal mechanism of protection. Thus, immunogenicity assessments in vaccine trials have focused on measurements of antibody responses to the vaccine. Non-inferiority of antibody responses after two doses of HPV vaccines separated by 6 months has been demonstrated and this evidence supported the recent WHO recommendations for two-dose vaccination schedules in both boys and girls 9-14 years of age. There is also some evidence suggesting that one dose of HPV vaccines may provide protection similar to the currently recommended two-dose regimens but robust data on efficacy and immunogenicity of one-dose vaccine schedules are lacking. In addition, immunogenicity has been assessed and reported using different methods, precluding direct comparison of results between different studies and vaccines. New head-to-head vaccine trials evaluating one-dose immunogenicity and efficacy have been initiated and an increase in the number of trials relying on immunobridging is anticipated. Therefore, standardized measurement and reporting of immunogenicity for the up to nine HPV types targeted by the current vaccines is now critical. Building on previous HPV serology assay standardization and harmonization efforts initiated by the WHO HPV LabNet in 2006, new secondary standards, critical reference reagents and testing guidelines will be generated as part of a new partnership to facilitate harmonization of the immunogenicity testing in new HPV vaccine trials.

Optimizing a Human Papillomavirus Type 16 L1-Based Chimaeric Gene for Expression in Plants

Human papillomaviruses (HPVs) are the causative agents of cervical cancer, the fourth most prevalent cancer in women worldwide. The major capsid protein L1 self-assembles into virus-like particles (VLPs), even in the absence of the minor L2 protein: such VLPs have successfully been used as prophylactic vaccines. There remains a need, however, to develop cheaper vaccines that protect against a wider range of HPV types. The use of all or parts of the L2 minor capsid protein can potentially address this issue, as it has sequence regions conserved across several HPV types, which can elicit a wider spectrum of cross-neutralizing antibodies. Production of HPV VLPs in plants is a viable option to reduce costs; the use of a L1/L2 chimera which has previously elicited a cross-protective immune response is an option to broaden cross-protection. The objective of this study was to investigate the effect of codon optimization and of increasing the G+C content of synthetic L1/L2 genes on protein expression in plants. Additionally, we replaced varying portions of the 5' region of the L1 gene with the wild type (wt) viral sequence to determine the effect of several negative regulatory elements on expression. We showed that GC-rich genes resulted in a 10-fold increase of mRNA levels and 3-fold higher accumulation of proteins. However, the highest increase of expression was achieved with a high GC-content human codon-optimized gene, which resulted in a 100-fold increase in mRNA levels and 8- to 9-fold increase in protein levels. Changing the 5' end of the L1 gene back to its wt sequence decreased mRNA and protein expression. Our results suggest that the negative elements in the 5' end of L1 are inadvertently destroyed by changing the codon usage, which enhances protein expression.

Cellular Immune Responses 6 Years Following 1, 2, or 3 Doses of Quadrivalent HPV Vaccine in Fijian Girls and Subsequent Responses to a Dose of Bivalent HPV Vaccine

Background

This study examined the cellular immunity of 0, 1, 2, and 3 doses of Gardasil vaccine (4vHPV) in girls after 6 years and their responses to a subsequent dose of Cervarix vaccine (2vHPV).

Methods

A subset of girls (n = 59) who previously received 0, 1, 2, or 3 doses of 4vHPV 6 years earlier were randomly selected from a cohort study of Fijian girls (age 15-19 years). Blood was collected before and 28 days after a dose of 2vHPV. The HPV16- and HPV18-specific cellular immune response was determined by IFNγ-ELISPOT and by measurement of cytokines in peripheral blood mononuclear cell supernatants.

Results

Six years after 4vHPV vaccination, HPV18-specific responses were significantly lower in the 1- (1D) or 2-dose (2D) recipients compared with 3-dose recipients (2D: IFNγ-ELISPOT: P = .008; cytokines, IFNγ: P = .002; IL-2: P = .022; TNFα: P = .016; IL-10: P = .018; 1D: IL-2: P = .031; IL-10: P = .014). These differences were no longer significant post-2vHPV. No significant differences in HPV16 responses (except IL-2, P < .05) were observed between the 2- or 1-dose recipients and 3-dose recipients.

Conclusions

These data suggest that cellular immunity following reduced-dose schedules was detectable after 6 years, although the responses were variable between HPV types and dosage groups. The clinical significance of this is unknown. Further studies on the impact of reduced dose schedules are needed, particularly in high-disease burden settings.

Seropositivity to non-vaccine incorporated genotypes induced by the bivalent and quadrivalent HPV vaccines: A systematic review and meta-analysis

BACKGROUND

Human papillomavirus vaccines have demonstrated remarkable efficacy against persistent infection and disease associated with vaccine-incorporated genotypes and a degree of efficacy against some genetically related, non-vaccine-incorporated genotypes. The vaccines differ in the extent of cross-protection against these non-vaccine genotypes. Data supporting the role for neutralizing antibodies as a correlate or surrogate of cross-protection are lacking, as is a robust assessment of the seroconversion rates against these non-vaccine genotypes.

METHODS

We performed a systematic review and meta-analysis of available data on vaccine-induced neutralizing antibody seropositivity to non-vaccine incorporated HPV genotypes.

RESULTS

Of 304 articles screened, 9 were included in the analysis representing ca. 700 individuals. The pooled estimate for seropositivity against HPV31 for the bivalent vaccine (86%; 95%CI 78-91%) was higher than that for the quadrivalent vaccine (61%; 39-79%; p=0.011). The pooled estimate for seropositivity against HPV45 for the bivalent vaccine (50%; 37-64%) was also higher than that for the quadrivalent vaccine (16%; 6-36%; p=0.007). Seropositivity against HPV33, HPV52 and HPV58 were similar between the vaccines. Mean seropositivity rates across non-vaccine genotypes were positively associated with the corresponding vaccine efficacy data reported from vaccine trials.

CONCLUSIONS

These data improve our understanding of vaccine-induced functional antibody specificity against non-vaccine incorporated genotypes and may help to parameterize vaccine-impact models and improve patient management in a post-vaccine setting.

Cryoelectron Microscopy Maps of Human Papillomavirus 16 Reveal L2 Densities and Heparin Binding Site

Human papillomavirus (HPV) is a significant health burden and leading cause of virus-induced cancers. The current commercial vaccines are genotype specific and provide little therapeutic benefit to patients with existing HPV infections. Host entry mechanisms represent an excellent target for alternative therapeutics, but HPV receptor use, the details of cell attachment, and host entry are inadequately understood. Here we present near-atomic resolution structures of the HPV16 capsid and HPV16 in complex with heparin, both determined from cryoelectron micrographs collected with direct electron detection technology. The structures clarify details of capsid architecture for the first time, including variation in L1 major capsid protein conformation and putative location of L2 minor protein. Heparin binds specifically around the capsid icosahedral vertices and may recapitulate the earliest stage of infection, providing a framework for continuing biochemical, genetic, and biophysical studies.

The economic evaluation of human papillomavirus vaccination strategies against cervical cancer in women in Lao PDR: a mathematical modelling approach

BACKGROUND

Cervical cancer, a preventable disease, is the third leading cause of cancer morbidity and mortality in the Lao People's Democratic Republic (Lao PDR). Since many cervical cancers are linked to human papilloma virus (HPV) infection, vaccination against this virus may lead to a reduction in these types of cancer. The study described here is the first to compare the cost-effectiveness of different HPV vaccination options in Lao PDR.

METHODS

A dynamic compartment model was created. The model included routine screening activities already in place, as well as theoretical interventions that included a 10-year old girl-only vaccination programme combined with/without a 10-year old boy vaccination programme and/or a catch-up component. The simulation was run over 100 years. In base case analyses, we assumed 70 % vaccination coverage with lifelong protection and 100 % efficacy against HPV types 16/18. The outcomes of interest were the incremental cost per Disability-Adjusted Life Year (DALY) averted.

RESULTS

In base case analyses, according to the WHO definition of cost-effectiveness thresholds, vaccinating 10-year-old girls was very cost-effective. Adding a catch-up vaccination element for females aged 11-25 years was also very cost-effective, costing 1559 international dollars (I$) per DALY averted. Increasing the age limit of the catch-up vaccination component to 75 years old showed that this remained a cost-effective option (I$ 5840 per DALY averted). Adding a vaccination programme for 10-year-old boys was not found to be cost-effective unless a short time simulation (30 years or less) was considered, along with a catch-up vaccination component for both males and females.

CONCLUSIONS

Adding a catch-up female vaccination component is more attractive than adding a 10-year-old boy vaccination component.

Is HPV vaccination in pregnancy safe?

Millions of doses of HPV vaccine have been administered globally. Inadvertent administration of HPV vaccine during pregnancy occurs given that the main recipients of the vaccine are fertile young women, who might be unaware of their pregnancy at the time of their vaccination. To investigate the subject of HPV vaccine and pregnancy , the databases of PubMed and Embase were searched to find the relevant literature published in English within the last 10 y. Most of the evidence pertaining to fetal adverse events following HPV vaccination relates to spontaneous miscarriage. None of the relevant studies found any significantly increased rate of spontaneous abortion in the overall analyses. There was no indication of other HPV vaccine-associated adverse events in pregnancy or immediately post-conception.