Cost-effectiveness of treating all hepatitis B-positive individuals in the United States.

Chronic hepatitis B virus (HBV) infection is a leading cause of liver disease and related mortality globally. However, most of the infected individuals in the United States remain undiagnosed and untreated. There is a need to understand more completely the economic and disease burden impact of removing treatment restrictions and increasing diagnosis and treatment. The PRoGReSs model, a dynamic HBV model that tracks the infected population by year, disease stage, and gender, was used to quantify the disease and economic burden of chronic HBV infection in the United States from 2020 to 2050 based on four scenarios: a status quo (base) scenario and three treat-all scenarios, in which screening, diagnosis, and treatment were maximized at different annual treatment price levels of $5382, $2000 and $750. Compared to the base scenario, the treat-all scenarios would avert 71,100 acute and 11,100 chronic incident cases of HBV, and 169,000 liver-related deaths from 2020 to 2050. At an annual treatment cost of $2000, treating all HBV infections would be highly cost-effective, and at $750 would be cost saving and would achieve a positive return on investment before 2050. Maximizing the diagnosed and treated HBV population in the United States would avert a significant number of cases of advanced liver disease and related mortality. Such interventions can also be cost-effective compared to the status quo strategy, and cost saving at a treatment price threshold of $750 annually, above the current lowest annual treatment cost of $362.

The impact of immigration on hepatitis B burden in the United States: a modelling study.

Background: The 2016 World Health Assembly endorsed the elimination of hepatitis B virus (HBV) infections by 2030. However, the HBV prevalence in Western countries, where the historical prevalence is low and highly impacted by immigration trends, remains uncertain making planning difficult. We aimed to develop a more accurate estimate of HBV prevalence and identify key immigrant populations that need to be screened, vaccinated, and treated to achieve the elimination targets. Methods: US immigration data from 1900 forward and country-specific modeled prevalence by age and sex were used to estimate immigrated HBV infections entering the US, new infections in the US, mortality (all-cause and liver-related), and disease burden through 2030. Findings: Using a dynamic Markov model, we estimated 1.8 million (95% uncertainty interval: 1.3-2.6 million) HBV infections in 2020 in all ages, higher than the NHANES national serosurvey. Infections between ages 30-74 accounted for 82% of all cases. Furthermore, HBV infections were concentrated among immigrants. New decompensated cirrhosis, hepatocellular carcinoma, and liver related deaths are expected to increase by 20%, 31% and 25% respectively from 2019 to 2030 at current diagnosis and treatment rate. Interpretation: National serosurveys can underestimate total infections due to under-sampling in immigrant populations. To meet the WHO elimination targets, culturally appropriate screening and linkage to care programs in the immigrant populations are needed in the US. In their absence, there will be significant increases in the burden of HBV and the US will fail to meet the elimination targets by 2030. Funding: This analysis was funded by a research grant from Gilead Sciences (IN-US-988-5786) and made possible by grants from John C Martin Foundation (2019-G024), ZeShan Foundation (2021-0101-1-CDA-HEP-10), and EndHep2030 who supported country analyses.

Impacts of the Egyptian national screening and treatment programme for viral hepatitis C: A cost-effectiveness model.

BACKGROUND & AIMS: Egypt used to have one of the highest prevalences of HCV infection worldwide. The Egyptian Ministry of Health launched a national campaign for the detection and management of HCV to reduce its burden. This study aims to carry out a cost-effectiveness analysis to evaluate the costs and benefits of the Egyptian national screening and treatment programme. METHODS: A disease burden and economic impact model was populated with the Egyptian national screening and treatment programme data to assess direct medical costs, health effects measured in disability-adjusted life years and the incremental cost-effectiveness ratio. The scenario was compared to a historical base case, which assumed that no programme had been conducted. RESULTS: Total number of viremic cases is expected to decrease in 2030 by 86% under the national screening and treatment programme, versus by 41% under the historical base case. Annual discounted direct medical costs are expected to decrease from $178 million in 2018 to $81 million by 2030 under the historical base case, while annual direct medical costs are estimated to have peaked in 2019 at $312 million before declining to $55 million by 2030 under the national screening and treatment programme. Under the programme, annual disability-adjusted life years are expected to decline to 127 647 by 2030, leading to 883 333 cumulative disability-adjusted life years averted over 2018-2030. CONCLUSIONS: The national screening and treatment programme is highly cost-effective by the year 2021, cost-saving by 2029 and expected to save about $35 million in direct costs and $4705 million in indirect costs by 2030.

Hepatitis D double reflex testing of all hepatitis B carriers in low-HBV- and high-HBV/HDV-prevalence countries.

Hepatitis D virus (HDV) infection occurs as a coinfection with hepatitis B and increases the risk of hepatocellular carcinoma, decompensated cirrhosis, and mortality compared to hepatitis B virus (HBV) monoinfection. Reliable estimates of the prevalence of HDV infection and disease burden are essential to formulate strategies to find coinfected individuals more effectively and efficiently. The global prevalence of HBV infections was estimated to be 262,240,000 in 2021. Only 1,994,000 of the HBV infections were newly diagnosed in 2021, with more than half of the new diagnoses made in China. Our initial estimates indicated a much lower prevalence of HDV antibody (anti-HDV) and HDV RNA positivity than previously reported in published studies. Accurate estimates of HDV prevalence are needed. The most effective method to generate estimates of the prevalence of anti-HDV and HDV RNA positivity and to find undiagnosed individuals at the national level is to implement double reflex testing. This requires anti-HDV testing of all hepatitis B surface antigen-positive individuals and HDV RNA testing of all anti-HDV-positive individuals. This strategy is manageable for healthcare systems since the number of newly diagnosed HBV cases is low. At the global level, a comprehensive HDV screening strategy would require only 1,994,000 HDV antibody tests and less than 89,000 HDV PCR tests. Double reflex testing is the preferred strategy in countries with a low prevalence of HBV and those with a high prevalence of both HBV and HDV. For example, in the European Union and North America only 35,000 and 22,000 cases, respectively, will require anti-HDV testing annually.

Cost-effectiveness and economic investment to eliminate chronic hepatitis C in Mexico.

In July 2020, the Mexican Government initiated the National Program for Elimination of Hepatitis C (HCV) under a procurement agreement, securing universal, free access to HCV screening, diagnosis and treatment for 2020-2022. This analysis quantifies the clinical and economic burden of HCV (MXN) under a continuation (or end) to the agreement. A modelling and Delphi approach was used to evaluate the disease burden (2020-2030) and economic impact (2020-2035) of the Historical Base compared to Elimination, assuming the agreement continues (Elimination-Agreement to 2035) or terminates (Elimination-Agreement to 2022). We estimated cumulative costs and the per-patient treatment expenditure needed to achieve net-zero cost (the difference in cumulative costs between the scenario and the base). Elimination is defined as a 90% reduction in new infections, 90% diagnosis coverage, 80% treatment coverage and 65% reduction in mortality by 2030. A viraemic prevalence of 0.55% (0.50-0.60) was estimated on 1st January 2021, corresponding to 745,000 (95% CI 677,000-812,000) viraemic infections in Mexico. The Elimination-Agreement to 2035 would achieve net-zero cost by 2023 and accrue 31.2 billion in cumulative costs. Cumulative costs under the Elimination-Agreement to 2022 are estimated at 74.2 billion. Under Elimination-Agreement to 2022, the per-patient treatment price must decrease to 11,000 to achieve net-zero cost by 2035. The Mexican Government could extend the agreement through 2035 or reduce the cost of HCV treatment to 11,000 to achieve HCV elimination at net-zero cost.

Lives saved with vaccination for 10 pathogens across 112 countries in a pre-COVID-19 world.

Background: Vaccination is one of the most effective public health interventions. We investigate the impact of vaccination activities for Haemophilus influenzae type b, hepatitis B, human papillomavirus, Japanese encephalitis, measles, Neisseria meningitidis serogroup A, rotavirus, rubella, Streptococcus pneumoniae, and yellow fever over the years 2000-2030 across 112 countries. Methods: Twenty-one mathematical models estimated disease burden using standardised demographic and immunisation data. Impact was attributed to the year of vaccination through vaccine-activity-stratified impact ratios. Results: We estimate 97 (95%CrI[80, 120]) million deaths would be averted due to vaccination activities over 2000-2030, with 50 (95%CrI[41, 62]) million deaths averted by activities between 2000 and 2019. For children under-5 born between 2000 and 2030, we estimate 52 (95%CrI[41, 69]) million more deaths would occur over their lifetimes without vaccination against these diseases. Conclusions: This study represents the largest assessment of vaccine impact before COVID-19-related disruptions and provides motivation for sustaining and improving global vaccination coverage in the future. Funding: VIMC is jointly funded by Gavi, the Vaccine Alliance, and the Bill and Melinda Gates Foundation (BMGF) (BMGF grant number: OPP1157270 / INV-009125). Funding from Gavi is channelled via VIMC to the Consortium's modelling groups (VIMC-funded institutions represented in this paper: Imperial College London, London School of Hygiene and Tropical Medicine, Oxford University Clinical Research Unit, Public Health England, Johns Hopkins University, The Pennsylvania State University, Center for Disease Analysis Foundation, Kaiser Permanente Washington, University of Cambridge, University of Notre Dame, Harvard University, Conservatoire National des Arts et Métiers, Emory University, National University of Singapore). Funding from BMGF was used for salaries of the Consortium secretariat (authors represented here: TBH, MJ, XL, SE-L, JT, KW, NMF, KAMG); and channelled via VIMC for travel and subsistence costs of all Consortium members (all authors). We also acknowledge funding from the UK Medical Research Council and Department for International Development, which supported aspects of VIMC's work (MRC grant number: MR/R015600/1).JHH acknowledges funding from National Science Foundation Graduate Research Fellowship; Richard and Peggy Notebaert Premier Fellowship from the University of Notre Dame. BAL acknowledges funding from NIH/NIGMS (grant number R01 GM124280) and NIH/NIAID (grant number R01 AI112970). The Lives Saved Tool (LiST) receives funding support from the Bill and Melinda Gates Foundation.This paper was compiled by all coauthors, including two coauthors from Gavi. Other funders had no role in study design, data collection, data analysis, data interpretation, or writing of the report. All authors had full access to all the data in the study and had final responsibility for the decision to submit for publication.

Progress towards hepatitis C virus elimination in high-income countries: An updated analysis.

BACKGROUND & AIMS: Elimination of HCV by 2030, as defined by the World Health Organization (WHO), is attainable with the availability of highly efficacious therapies. This study reports progress made in the timing of HCV elimination in 45 high-income countries between 2017 and 2019. METHODS: Disease progression models of HCV infection for each country were updated with latest data on chronic HCV prevalence, and annual diagnosis and treatment levels, assumed to remain constant in the future. Modelled outcomes were analysed to determine the year in which each country would meet the WHO 2030 elimination targets. RESULTS: Of the 45 countries studied, 11 (Australia, Canada, France, Germany, Iceland, Italy, Japan, Spain, Sweden, Switzerland, and United Kingdom) are on track to meet WHO's elimination targets by 2030; five (Austria, Malta, Netherlands, New Zealand, and South Korea) by 2040; and two (Saudi Arabia and Taiwan) by 2050. The remaining 27 countries are not expected to achieve elimination before 2050. Compared to progress in 2017, South Korea is no longer on track to eliminate HCV by 2030, three (Canada, Germany, and Sweden) are now on track, and most countries (30) saw no change. CONCLUSIONS: Assuming high-income countries will maintain current levels of diagnosis and treatment, only 24% are on track to eliminate HCV by 2030, and 60% are off track by at least 20 years. If current levels of diagnosis and treatment continue falling, achieving WHO's 2030 targets will be more challenging. With less than ten years remaining, screening and treatment expansion is crucial to meet WHO's HCV elimination targets.

Estimating the health impact of vaccination against ten pathogens in 98 low-income and middle-income countries from 2000 to 2030: a modelling study.

BACKGROUND: The past two decades have seen expansion of childhood vaccination programmes in low-income and middle-income countries (LMICs). We quantify the health impact of these programmes by estimating the deaths and disability-adjusted life-years (DALYs) averted by vaccination against ten pathogens in 98 LMICs between 2000 and 2030. METHODS: 16 independent research groups provided model-based disease burden estimates under a range of vaccination coverage scenarios for ten pathogens: hepatitis B virus, Haemophilus influenzae type B, human papillomavirus, Japanese encephalitis, measles, Neisseria meningitidis serogroup A, Streptococcus pneumoniae, rotavirus, rubella, and yellow fever. Using standardised demographic data and vaccine coverage, the impact of vaccination programmes was determined by comparing model estimates from a no-vaccination counterfactual scenario with those from a reported and projected vaccination scenario. We present deaths and DALYs averted between 2000 and 2030 by calendar year and by annual birth cohort. FINDINGS: We estimate that vaccination of the ten selected pathogens will have averted 69 million (95% credible interval 52-88) deaths between 2000 and 2030, of which 37 million (30-48) were averted between 2000 and 2019. From 2000 to 2019, this represents a 45% (36-58) reduction in deaths compared with the counterfactual scenario of no vaccination. Most of this impact is concentrated in a reduction in mortality among children younger than 5 years (57% reduction [52-66]), most notably from measles. Over the lifetime of birth cohorts born between 2000 and 2030, we predict that 120 million (93-150) deaths will be averted by vaccination, of which 58 million (39-76) are due to measles vaccination and 38 million (25-52) are due to hepatitis B vaccination. We estimate that increases in vaccine coverage and introductions of additional vaccines will result in a 72% (59-81) reduction in lifetime mortality in the 2019 birth cohort. INTERPRETATION: Increases in vaccine coverage and the introduction of new vaccines into LMICs have had a major impact in reducing mortality. These public health gains are predicted to increase in coming decades if progress in increasing coverage is sustained. FUNDING: Gavi, the Vaccine Alliance and the Bill & Melinda Gates Foundation.

Global prevalence of hepatitis C virus in women of childbearing age in 2019: a modelling study.

BACKGROUND: Treatment for infection with hepatitis C virus (HCV) during pregnancy has not yet been approved; however, interventions specifically targeting women, especially those of childbearing age (15-49 years), could prevent vertical transmission and community spread. To assess the impact of such interventions, improved prevalence estimates in this group are needed. We aimed to estimate the global prevalence of viraemic HCV in 2019 among women of childbearing age. METHODS: In this modelling study, we used previously developed models for 110 countries inputted with country-specific demographic and HCV epidemiology data. We did a literature review, searching PubMed, Embase, and grey literature for studies published between Jan 1, 2000, and June 30, 2018, reporting HCV antibody or viraemic prevalence in women of childbearing age. Studies from the literature review and studies in models were compared by use of a data quality scoring system and models were updated, as appropriate, when a better study was identified. We used these HCV disease burden models to calculate the 2019 prevalence of viraemic HCV in women of childbearing age. In countries without a model, prevalence was extrapolated by Global Burden of Disease (GBD) region. FINDINGS: An estimated 14 860 000 (95% uncertainty interval [UI] 9 667 000-18 282 000) women aged 15-49 years had HCV infection worldwide in 2019, corresponding to a viraemic prevalence of 0·78% (95% UI 0·62-0·86). Globally, HCV prevalence increased with age, rising from 0·25% (95% UI 0·20-0·27) in women aged 15-19 years to 1·21% (0·97-1·34) in women aged 45-49 years. China (16% of total infections) and Pakistan (15%) had the greatest numbers of viraemic infections, but viraemic prevalence was highest in Mongolia (5·14%, 95% CI 3·46-6·28) and Burundi (4·91%, 3·80-18·75). Of the countries with 500 cases or more, viraemic prevalence was lowest in Chile (0·07%, 95% UI 0·04-0·12). Among the GBD regions, eastern Europe had the highest viraemic prevalence (3·39%, 95% UI 1·88-3·54). By WHO region, the Eastern Mediterranean region had the highest viraemic prevalence (1·75%, 95% UI 1·26- 1·90). INTERPRETATION: Most research on HCV disease burden among women aged 15-49 years focuses on pregnant women. Using modelling, this analysis provides global and national estimates of HCV prevalence in all women of childbearing age. These data can inform preconception test-and-treat strategies to reduce vertical transmission and total disease burden. FUNDING: Gilead Sciences, John C Martin Foundation, private donors.

Impact of COVID-19 on global HCV elimination efforts.

BACKGROUND & AIMS: Coronavirus disease 2019 (COVID-19) has placed a significant strain on national healthcare systems at a critical moment in the context of hepatitis elimination. Mathematical models can be used to evaluate the possible impact of programmatic delays on hepatitis disease burden. The objective of this analysis was to evaluate the incremental change in HCV liver-related deaths and liver cancer, following a 3-month, 6-month, or 1-year hiatus in hepatitis elimination programs. METHODS: Previously developed models were adapted for 110 countries to include a status quo or 'no delay' scenario and a '1-year delay' scenario assuming significant disruption in interventions (screening, diagnosis, and treatment) in the year 2020. Annual country-level model outcomes were extracted, and weighted averages were used to calculate regional (WHO and World Bank Income Group) and global estimates from 2020 to 2030. The incremental annual change in outcomes was calculated by subtracting the 'no-delay' estimates from the '1-year delay' estimates. RESULTS: The '1-year delay' scenario resulted in 44,800 (95% uncertainty interval [UI]: 43,800-49,300) excess hepatocellular carcinoma cases and 72,300 (95% UI: 70,600-79,400) excess liver-related deaths, relative to the 'no-delay' scenario globally, from 2020 to 2030. Most missed treatments would be in lower-middle income countries, whereas most excess hepatocellular carcinoma and liver-related deaths would be among high-income countries. CONCLUSIONS: The impact of COVID-19 extends beyond the direct morbidity and mortality associated with exposure and infection. To mitigate the impact on viral hepatitis programming and reduce excess mortality from delayed treatment, policy makers should prioritize hepatitis programs as soon as it becomes safe to do so. LAY SUMMARY: COVID-19 has resulted in many hepatitis elimination programs slowing or stopping altogether. A 1-year delay in hepatitis diagnosis and treatment could result in an additional 44,800 liver cancers and 72,300 deaths from HCV globally by 2030. Countries have committed to hepatitis elimination by 2030, so attention should shift back to hepatitis programming as soon as it becomes appropriate to do so.

Modelling hepatitis B virus infection and impact of timely birth dose vaccine: A comparison of two simulation models.

Hepatitis B is a global epidemic that requires carefully orchestrated vaccination initiatives in geographical regions of medium to high endemicity to reach the World Health Organization's elimination targets by 2030. This study compares two widely-used deterministic hepatitis B models-the Imperial HBV model and the CDA Foundation's PRoGReSs-based on their predicted outcomes in four countries. The impact of scaling up of the timely birth dose of the hepatitis B vaccine is also investigated. The two models predicted largely similar outcomes for the impact of vaccination programmes on the projected numbers of new cases and deaths under high levels of the infant hepatitis B vaccine series. However, scenarios for the scaling up of the infant hepatitis B vaccine series had a larger impact in the PRoGReSs model than in the Imperial model due to the infant vaccine series directly leading to the reduction of perinatal transmission in the PRoGReSs model, but not in the Imperial model. Meanwhile, scaling up of the timely birth dose vaccine had a greater impact on the outcomes of the Imperial hepatitis B model than in the PRoGReSs model due to the greater protection that the birth dose vaccine confers to infants in the Imperial model compared to the PRoGReSs model. These differences underlie the differences in projections made by the models under some circumstances. Both sets of assumptions are consistent with available data and reveal a structural uncertainty that was not apparent in either model in isolation. Those relying on projections from models should consider outputs from both models and this analysis provides further evidence of the benefits of systematic model comparison for enhancing modelling analyses.

Optimization of hepatitis C virus screening strategies by birth cohort in Italy.

BACKGROUND AND AIMS: Cost-effective screening strategies are needed to make hepatitis C virus (HCV) elimination a reality. We determined if birth cohort screening is cost-effective in Italy. METHODS: A model was developed to quantify screening and healthcare costs associated with HCV. The model-estimated prevalence of undiagnosed HCV was used to calculate the antibody screens needed annually, with a €25 000 cost-effectiveness threshold. Outcomes were assessed under the status quo and a scenario that met the World Health Organization's targets for elimination of HCV. The elimination scenario was assessed under five screening strategies. RESULTS: A graduated birth cohort screening strategy (graduated screening 1: 1968-1987 birth cohorts, then expanding to 1948-1967 cohorts) was the least costly. This strategy would gain approximately 144 000 quality-adjusted life years (QALYs) by 2031 and result in an 89.3% reduction in HCV cases, compared to an 89.6%, 89.0%, 89.7% and 88.7% reduction for inversed graduated screening, 1948-77 birth cohort, 1958-77 birth cohort and universal screening, respectively. Graduated screening 1 yielded the lowest incremental cost-effectiveness ratio (ICER) of €3552 per QALY gained. CONCLUSIONS: In Italy, a graduated screening scenario is the most cost-effective strategy. Other countries could consider a similar birth cohort approach when developing HCV screening strategies.

Global prevalence of hepatitis C virus in children in 2018: a modelling study.

BACKGROUND: Hepatitis C virus (HCV) prevalence estimates for adults and high-risk groups have been widely published, but the disease burden in children is poorly understood. Direct-acting antiviral drugs, which are considered to be highly effective curative therapies for HCV, are now approved for paediatric patients as young as 3 years. Reliable prevalence estimates for this population are needed to inform scale-up of treatment and national strategies. This analysis combines past modelling and epidemiological work in 104 countries and territories to estimate global HCV prevalence in children in 2018. METHODS: In this modelling study, a comprehensive literature review for articles published between Jan 1, 2000, and March 31, 2019, was used to determine historical HCV prevalence estimates in children in all 249 countries and territories of the world. We identified published HCV prevalence estimates for children aged 0-18 years who are not at high risk of HCV infection in 39 countries and territories and inputted them into dynamic Markov disease-burden models to estimate viraemic HCV prevalence in 2018. For 25 of them, which had complete data, available information on HCV prevalence in children was used to build regression models to predict paediatric prevalence in an additional 65 countries and territories that had country-specific or territory-specific data about predictors only. Regression models were created for each 5-year paediatric age cohort from 0 to 19 years, considering several predictor variables. The data and forecasts from the 104 countries and territories for which data were available were used to calculate HCV prevalence by Global Burden of Disease region, which was then applied to the remaining 145 countries and territories to generate a global estimate. FINDINGS: The global estimate for viraemic prevalence in the paediatric population aged 0-18 years was 0·13% (95% uncertainty interval 0·08-0·16), corresponding to 3·26 million (2·07-3·90) children with HCV in 2018. HCV prevalence increased with age in all countries and territories. HCV prevalence in women of childbearing age was the strongest predictor of HCV prevalence in children aged 0-4 years (p<0·0001). Prevalence of HCV in adults was significantly associated with HCV prevalence in children aged 5-19 years (p<0·0001), and the proportion of HCV infections in people who inject drugs was significantly associated with HCV prevalence in children aged 15-19 years (p=0·036). INTERPRETATION: Most studies on HCV prevalence in children focus on high-risk groups and highly endemic geographic areas. Our analysis provides global prevalence estimates of HCV in the paediatric population. Treatment in paediatric patients requires different clinical and population health management optimisation than in adults. Because of this heterogeneity, country-specific or territory-specific and age-specific HCV prevalence estimates can help countries and territories to improve national HCV elimination strategies. FUNDING: Gilead Sciences, John C Martin Foundation, and private donors.

Forecasting Hepatitis C liver disease burden on real-life data. Does the hidden iceberg matter to reach the elimination goals?

BACKGROUND & AIMS: Advances in direct-acting antiviral treatment of HCV have reinvigorated public health initiatives aimed at identifying affected individuals. We evaluated the possible impact of only diagnosed and linked-to-care individuals on overall HCV burden estimates and identified a possible strategy to achieve the WHO targets by 2030. METHODS: Using a modelling approach grounded in Italian real-life data of diagnosed and treated patients, different linkage-to-care scenarios were built to evaluate potential strategies in achieving the HCV elimination goals. RESULTS: Under the 40% linked-to-care scenario, viraemic burden would decline (60%); however, eligible patients to treat will be depleted by 2025. Increased case finding through a targeted screening strategy in 1948-1978 birth cohorts could supplement the pool of diagnosed patients by finding 75% of F0-F3 cases. Under the 60% linked-to-care scenario, viraemic infections would decline by 70% by 2030 but the patients eligible for treatment will run out by 2028. If treatment is to be maintained, a screening strategy focusing on 1958-1978 birth cohorts could capture 55% of F0-F3 individuals. Under the 80% linked-to-care scenario, screening limited in 1968-1978 birth cohorts could sustain treatment at levels required to achieve the HCV elimination goals. CONCLUSION: In Italy, which is an HCV endemic country, the eligible pool of patients to treat will run out between 2025 and 2028. To maintain the treatment rate and achieve the HCV elimination goals, increased case finding in targeted, high prevalence groups is required.