- Email: [email protected]
Defining control of HIV epidemics
Viewpoint
Defining control of HIV epidemics Alison P Galvani, Abhishek Pandey, Meagan C Fitzpatrick, Jan Medlock, Glenda E Gray
Although the HIV pandemic remains a global crisis, much progress has been made in implementing programmes to treat and prevent HIV infection. To guide prioritisation of efforts, the metric by which a country can declare its HIV epidemic as controlled has become increasingly relevant. Herein, we evaluate the merits of the four control criteria proposed by UNAIDS: percentage reduction in incidence over time; ratio of incidence to mortality; ratio of incidence to prevalence; and annual incidence. Using a transmission model to generate projections of demography, incidence, and mortality, we highlight potential pitfalls associated with each of the first three criteria. A definition of control based on annual incidence would provide clarity and consistency across settings.
Introduction Every day, nearly 5000 people are infected with HIV worldwide.1 This amount would be even higher if it were not for the extraordinary efforts of local, national, and international agencies. As progress continues towards widespread implementation of treatment-as-prevention programmes, the metric by which HIV control should be measured is becoming increasingly pertinent. So-called epidemic control criteria are integral to assessment of progress, geographical prioritisation of resources, and decisions regarding programmatic scaleup. An October, 2017, meeting convened by UNAIDS discussed four potential criteria: percentage reduction in incidence over time; ratio of incidence to mortality; ratio of incidence to prevalence; and annual incidence.2 Here, we assess the utility of each metric in the context of sub-Saharan Africa, the multinational region most profoundly affected by HIV. Specifically, we simulated trajectories of incidence, prevalence, and mortality with a model of HIV trans mission tailored to individual countries and their respective rates of diagnosis, treatment, and viral suppression.3 In each country, we compared performance according to each of the four criteria up until 2030, examining potential pitfalls in interpretation. UNAIDS has previously declared that a 90% reduction in incidence from 2010 in each country would “end the AIDS epidemic as a public health threat”.4 Incidence reduction is an appropriate measurement of progress, but not of control. Although a 90% reduction would result in very low incidences in many countries, some countries would still have unacceptably high HIV incidences. For example, a 90% reduction in annual incidence would correspond to 0∙14 per 10 000 in Niger and 21 per 10 000 in Lesotho (figure 1). After a 90% reduction, 2030 incidence in Lesotho would be higher than incidence in 2010 in Niger, where the HIV epidemic would clearly not have been defined as controlled.
Incidence-to-mortality ratio The incidence-to-mortality ratio (IMR) is based on the rationale that as the annual incidence of HIV drops to less than the annual mortality of people with HIV, the total number of people with HIV will decline. For most
countries in sub-Saharan Africa, we found that an IMR of less than 1 is also indicative of falling incidence. As a notable exception, however, the IMR criterion would be met in South Africa by 2020 despite projections of devastatingly high and mounting incidence of HIV (figure 2). The interplay between epidemiological dynamics, HIV progression, and demographic processes is projected to drive a rapid rise in mortality over the next few years in South Africa. This bolus of mortality permits the target incidence considered to indicate control to likewise increase. Under status quo interventions, which achieve 86% diagnosis of people with HIV, 65% treatment of diagnosed people with HIV, and 81% viral suppression of treated people with HIV, annual incidence will rise to 000 new infections by 2035, equivalent to over 358
Lancet HIV 2018 Published Online October 9, 2018 http://dx.doi.org/10.1016/ S2352-3018(18)30178-4 Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, CT, USA (Prof A P Galvani PhD, A Pandey PhD, M C Fitzpatrick PhD); Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, MD, USA (M C Fitzpatrick); Department of Biomedical Sciences, Oregon State University, Corvallis, Oregon, USA (J Medlock PhD); and Office of the President, South African Medical Research Council, Tygerberg, South Africa (G E Gray MD)
Incidence per 10 000 people
≤0·01
0·02
0·05
0·10
0·20
0·50
1·00
2·00
5·00
10·00
≥20·00
Figure 1: Country-specific control targets for Africa based on a 90% reduction in incidence from 2010 to 2030 Incidence rates converted by use of projected population size for 2030.
www.thelancet.com/hiv Published online October 9, 2018 http://dx.doi.org/10.1016/ S2352-3018(18)30178-4
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A 1·12 365
360
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1·04 350 Annual incidence Annual mortality Incidence-to-mortality ratio
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1·200 2018
Incidence-to-mortality ratio
Annual incidence or mortality (millions)
1·350
1·98
2022
2026 Time (year)
2030
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Figure 2: Predicted annual incidence, mortality, and incidence-to-mortality ratio in (A) South Africa and (B) sub-Saharan Africa Projections were generated with a previously validated country-specific model of HIV transmission, diagnosis, treatment, and viral suppression.3 At both national and international scales, the incidence-to-mortality ratio criterion (right axes) is met despite rising incidence. Correspondence to: Prof Alison P Galvani, Epidemiology of Microbial Diseases, Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, CT 06510, USA [email protected] For the US President’s Emergency Plan for AIDS Relief see https://www.pepfar.gov/
2
104 per 10 000 people (figure 2). Nonetheless, this epidemic would be considered controlled according to the IMR criterion, because the projected mortality of people with HIV—over 363 000 deaths in 2035—is even higher than the incidence. Similar dynamics are projected for sub-Saharan Africa overall with mortality outpacing incidence, thereby satisfying the IMR criterion despite the rising incidence (figure 2). In contrast to expectations that increasing mortality among people with HIV will make it easy to meet the IMR criterion in the short term, longer-term population trends could conversely cause the IMR to rise irrespective
of incidence. Sub-Saharan Africa is experiencing a so-called youth bulge, with more than half of the population younger than 20 years.5 Even if young people become infected with HIV at lower rates than in preceding age cohorts, alarmingly high mortality among older individuals would become necessary to compensate for the demographic imbalance and thereby reduce the IMR to less than 1. To avoid this nonsensical objective, the US President’s Emergency Plan for AIDS Relief specifies that treatment coverage must exceed 70% in its IMR based definition of control. This caveat makes the IMR currently inapplicable to 35 of the 38 sub-Saharan African countries we assessed. Additionally, within the 13 high-burden countries prioritised by the US president’s emergency plan, only Côte D’Ivoire has an IMR of less than 1, yet treatment coverage is just 41%. These examples, com bined with the irregularities introduced by demography, underscore the limited utility of the IMR criterion in sub-Saharan Africa. For countries with an IMR already less than 1, the appearance of success even in the face of unacceptably high incidence could dampen the sense of urgency needed to forestall many new infections. From a financial perspective, the IMR could be useful for predicting national trends in the budgetary outlay required to treat people with HIV. From an epidemiological perspective, the IMR also approximates the effective reproductive number (RE), the average number of trans missions generated from a single infection. However, financial sustainability and RE are arguably both insuf ficient frameworks for epidemiological control. RE is com monly applied to ascertain whether transmission of an infectious disease will be perpetuated. At an RE threshold of less than 1, the epidemic will ultimately be eradicated. This metric is most appropriate for short-term infections, such as influenza and Ebola virus. Given the long duration of HIV infection, the delay between suppression of RE to less than 1 and elimination is commensurately protracted. New infections will continue to accrue throughout this timeframe. Transmission from even a small proportion of the existing 36∙7 million people with HIV6 results in many new infections year-on-year. As an illustration, consider a reduction of RE to 0∙9, at which elimination of the pandemic is eventually expected. In the next generation of transmission, a simple product of RE and the 36∙7 million people with HIV, would lead to 33∙0 million new infections. In the subsequent transmission generation, a further 29∙7 million infections would be anticipated, and 26∙7 million infections in the generation after that. Exacerbating the prolonged elimination phase, a lapse in intervention efforts at any point would cause a surge in growth of the epidemic.
Incidence-to-prevalence ratio In contrast to the IMR, the incidence-to-prevalence ratio (IPR) increases in response to high mortality among people with HIV; however, this ratio has its own potential problems. First, the value for the IPR that would
www.thelancet.com/hiv Published online October 9, 2018 http://dx.doi.org/10.1016/ S2352-3018(18)30178-4
Viewpoint
ubiquitously correspond to control is not clear. For a lifelong infection such as HIV, prevalence rises as life expectancy increases. As the life expectancy for an uninfected person can vary substantially across nations, an IPR indicative of low incidence in one context might translate to an unacceptably high incidence in another setting. Second, given that the denominator is an indication of the years lived with HIV, the IPR could be reduced either by an increase in life expectancy among people with HIV, or a drop in the average age at which infection is acquired. A reduction in the average age at which infection is acquired is both troubling and probable, given that the sub-Saharan African youth bulge is likely to reduce the average age of infection over the next decade, even as rates of HIV acquisition drop. As with the IMR, interpretation of the IPR would thus require disentangling the effects of demography and transmission, which diminishes the utility of the metric as a criterion for epidemic control.
Incidence-based criteria Incidence-based criteria would circumvent the short comings of the IMR and the IPR and have several advantages. First, these criteria are unaffected by fluctuations in mortality rates in people with HIV, whether driven by trajectories of impending HIV mortality or from less foreseeable events such as natural disasters or civil unrest that disrupt infrastructure of the health-care systems. Second, although the other proposed criteria require robust measures of multiple variables, milestones based directly on current incidence minimise empirical uncertainty. Thirdly, whereas incidence metrics have a straightforward meaning worldwide, the value of a ratio or proportion does not convey a sense of the magnitude of the public health problem. Incidence-based criteria would also be consistent with WHO’s definition for control of mother-to-child transmission of HIV.7 We support defining HIV control as incidence less than one in 10 000 people per year. This incidence metric is concordant with the standard used by WHO to define control for other diseases.8 Temporal milestones could include a reduction to one in 1000 by 2030, and to one in 10 000 by 2035. In practice, these targets often align with the 90% based reductions in incidence recommended by UNAIDS.4 For example, the 2030 milestone would represent a 91∙3% drop from the current 11∙5 per 1000 capita incidence in South Africa.6 As the impending youth bulge drives population growth, a steady national incidence rate could translate to a rising case count. However, absolute case counts require the context of population size for interpretation of risk, making the incidence rate a more comprehensive metric of control across settings.
Conclusion An appropriate definition of control for national HIV epidemics is essential to galvanise programme scale-up
and to optimise the implementation of interventions. Control criteria should have applicability to every country worldwide, particularly to those areas that are hardest hit, such as South Africa. Vigilance will be important to achieving these control targets, and should be maintained even after they are fulfilled. Sustainable control will require long-term investment in programmes ensuring access to early diagnosis, rapid transition into care, and lifetime support for an individual’s management of HIV. For any country-wide criteria, it should be acknowledged that national averages could hide worrisome trends at a cally or within more granular scale, either geographi high-risk groups. Efficiently achieving a low national incidence will undoubtedly involve targeted interventions within high-risk groups who might also be less likely to access services. Outreach to high-risk groups will be instrumental in effective treatment-as-prevention approaches and will ensure that control is steadily achieved at subpopulation levels and for the country overall. Despite the challenges still to be overcome to achieve worldwide control of HIV by any criteria, global financial assistance for the fight against HIV has fallen by more than 24% since 2012.9 Comprehensive control criteria can facilitate communi cation regarding the shortfall between available and required resources, guiding decision makers in the drive towards HIV control and, ultimately, elimination. Contributors APG conceptualised and drafted the Viewpoint and interpreted results. AP programmed the model and generated and interpreted the results. MCF contributed to writing, interpreted the results, drafted the response to reviewers’ comments, and did the literature search. JM programmed the model and interpreted the results. GEG contributed to writing. Declaration of interests We declare no competing interests. Acknowledgments The authors gratefully acknowledge funding from the National Institutes of Health (U01 GM15627 and U01 GM087719 for APG and AP; and 4T32AI007524-19 for MCF) and the Notsew Orm Sands Foundation (for APG, AP, and MCF). APG is also grateful for support from the Burnett and Stender Families Endowed Chair. The funders had no role in study design; in the collection, analysis, or interpretation of data; in the writing of the report; or in the decision to submit the paper for publication. References 1 UNAIDS. Ending AIDS: progress towards the 90–90–90 targets. 2017. http://www.unaids.org/sites/default/files/media_asset/ Global_AIDS_update_2017_en.pdf (accessed Jan 12, 2018). 2 UNAIDS. Making the end of AIDS real: consensus building around what we mean by ‘epidemic control’. 2017. http://www.unaids.org/ sites/default/files/media_asset/glion_oct2017_meeting_report_en. pdf (accessed Feb 5, 2018). 3 Medlock J, Pandey A, Parpia AS, Tang A, Skrip LA, Galvani AP. Effectiveness of UNAIDS targets and HIV vaccination across 127 countries. Proc Natl Acad Sci USA 2017; 114: 4017–22. 4 UNAIDS. Fast track: ending the AIDS epidemic by 2030. 2014. http://www.unaids.org/sites/default/files/media_asset/JC2686_ WAD2014report_en.pdf (accessed March 30, 2017). 5 PopulationPyramid. Population pyramids of the world from 1950 to 2100. 2017. https://www.populationpyramid.net/sub-saharanafrica/2017 (accessed June 6, 2018). 6 UNAIDS. AIDSinfo. 2016. http://aidsinfo.unaids.org/ (accessed June 28, 2016).
www.thelancet.com/hiv Published online October 9, 2018 http://dx.doi.org/10.1016/ S2352-3018(18)30178-4
3
Viewpoint
7
8
4
WHO. Criteria and processes for validation: elimination of mother-to-child transmission of HIV and syphilis. 2014. http://apps. who.int/iris/bitstream/handle/10665/112858/9789241505888_eng.pdf;j sessionid=816397988645AD6AD6961F995158A4E0?sequence=1 (accessed Jan 12, 2018). WHO. Accelerating work to overcome the global impact of neglected tropical diseases. 2012. http://apps.who.int/iris/bitstream/handle/ 10665/70809/WHO_HTM_NTD_2012.1_eng.pdf?sequence=1 (accessed March 30, 2017).
9
Global Burden of Disease Health Financing Collaborator Network. Spending on health and HIV/AIDS: domestic health spending and development assistance in 188 countries, 1995–2015. Lancet 2018; 391: 1799–829.
© 2018 Elsevier Ltd. All rights reserved.
www.thelancet.com/hiv Published online October 9, 2018 http://dx.doi.org/10.1016/ S2352-3018(18)30178-4
Defining control of HIV epidemics Alison P Galvani, Abhishek Pandey, Meagan C Fitzpatrick, Jan Medlock, Glenda E Gray
Although the HIV pandemic remains a global crisis, much progress has been made in implementing programmes to treat and prevent HIV infection. To guide prioritisation of efforts, the metric by which a country can declare its HIV epidemic as controlled has become increasingly relevant. Herein, we evaluate the merits of the four control criteria proposed by UNAIDS: percentage reduction in incidence over time; ratio of incidence to mortality; ratio of incidence to prevalence; and annual incidence. Using a transmission model to generate projections of demography, incidence, and mortality, we highlight potential pitfalls associated with each of the first three criteria. A definition of control based on annual incidence would provide clarity and consistency across settings.
Introduction Every day, nearly 5000 people are infected with HIV worldwide.1 This amount would be even higher if it were not for the extraordinary efforts of local, national, and international agencies. As progress continues towards widespread implementation of treatment-as-prevention programmes, the metric by which HIV control should be measured is becoming increasingly pertinent. So-called epidemic control criteria are integral to assessment of progress, geographical prioritisation of resources, and decisions regarding programmatic scaleup. An October, 2017, meeting convened by UNAIDS discussed four potential criteria: percentage reduction in incidence over time; ratio of incidence to mortality; ratio of incidence to prevalence; and annual incidence.2 Here, we assess the utility of each metric in the context of sub-Saharan Africa, the multinational region most profoundly affected by HIV. Specifically, we simulated trajectories of incidence, prevalence, and mortality with a model of HIV trans mission tailored to individual countries and their respective rates of diagnosis, treatment, and viral suppression.3 In each country, we compared performance according to each of the four criteria up until 2030, examining potential pitfalls in interpretation. UNAIDS has previously declared that a 90% reduction in incidence from 2010 in each country would “end the AIDS epidemic as a public health threat”.4 Incidence reduction is an appropriate measurement of progress, but not of control. Although a 90% reduction would result in very low incidences in many countries, some countries would still have unacceptably high HIV incidences. For example, a 90% reduction in annual incidence would correspond to 0∙14 per 10 000 in Niger and 21 per 10 000 in Lesotho (figure 1). After a 90% reduction, 2030 incidence in Lesotho would be higher than incidence in 2010 in Niger, where the HIV epidemic would clearly not have been defined as controlled.
Incidence-to-mortality ratio The incidence-to-mortality ratio (IMR) is based on the rationale that as the annual incidence of HIV drops to less than the annual mortality of people with HIV, the total number of people with HIV will decline. For most
countries in sub-Saharan Africa, we found that an IMR of less than 1 is also indicative of falling incidence. As a notable exception, however, the IMR criterion would be met in South Africa by 2020 despite projections of devastatingly high and mounting incidence of HIV (figure 2). The interplay between epidemiological dynamics, HIV progression, and demographic processes is projected to drive a rapid rise in mortality over the next few years in South Africa. This bolus of mortality permits the target incidence considered to indicate control to likewise increase. Under status quo interventions, which achieve 86% diagnosis of people with HIV, 65% treatment of diagnosed people with HIV, and 81% viral suppression of treated people with HIV, annual incidence will rise to 000 new infections by 2035, equivalent to over 358
Lancet HIV 2018 Published Online October 9, 2018 http://dx.doi.org/10.1016/ S2352-3018(18)30178-4 Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, CT, USA (Prof A P Galvani PhD, A Pandey PhD, M C Fitzpatrick PhD); Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, MD, USA (M C Fitzpatrick); Department of Biomedical Sciences, Oregon State University, Corvallis, Oregon, USA (J Medlock PhD); and Office of the President, South African Medical Research Council, Tygerberg, South Africa (G E Gray MD)
Incidence per 10 000 people
≤0·01
0·02
0·05
0·10
0·20
0·50
1·00
2·00
5·00
10·00
≥20·00
Figure 1: Country-specific control targets for Africa based on a 90% reduction in incidence from 2010 to 2030 Incidence rates converted by use of projected population size for 2030.
www.thelancet.com/hiv Published online October 9, 2018 http://dx.doi.org/10.1016/ S2352-3018(18)30178-4
1
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A 1·12 365
360
1·08 1·06
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1·04 350 Annual incidence Annual mortality Incidence-to-mortality ratio
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Annual incidence or mortality (thousands)
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B 1·12
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1·200 2018
Incidence-to-mortality ratio
Annual incidence or mortality (millions)
1·350
1·98
2022
2026 Time (year)
2030
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Figure 2: Predicted annual incidence, mortality, and incidence-to-mortality ratio in (A) South Africa and (B) sub-Saharan Africa Projections were generated with a previously validated country-specific model of HIV transmission, diagnosis, treatment, and viral suppression.3 At both national and international scales, the incidence-to-mortality ratio criterion (right axes) is met despite rising incidence. Correspondence to: Prof Alison P Galvani, Epidemiology of Microbial Diseases, Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, CT 06510, USA [email protected] For the US President’s Emergency Plan for AIDS Relief see https://www.pepfar.gov/
2
104 per 10 000 people (figure 2). Nonetheless, this epidemic would be considered controlled according to the IMR criterion, because the projected mortality of people with HIV—over 363 000 deaths in 2035—is even higher than the incidence. Similar dynamics are projected for sub-Saharan Africa overall with mortality outpacing incidence, thereby satisfying the IMR criterion despite the rising incidence (figure 2). In contrast to expectations that increasing mortality among people with HIV will make it easy to meet the IMR criterion in the short term, longer-term population trends could conversely cause the IMR to rise irrespective
of incidence. Sub-Saharan Africa is experiencing a so-called youth bulge, with more than half of the population younger than 20 years.5 Even if young people become infected with HIV at lower rates than in preceding age cohorts, alarmingly high mortality among older individuals would become necessary to compensate for the demographic imbalance and thereby reduce the IMR to less than 1. To avoid this nonsensical objective, the US President’s Emergency Plan for AIDS Relief specifies that treatment coverage must exceed 70% in its IMR based definition of control. This caveat makes the IMR currently inapplicable to 35 of the 38 sub-Saharan African countries we assessed. Additionally, within the 13 high-burden countries prioritised by the US president’s emergency plan, only Côte D’Ivoire has an IMR of less than 1, yet treatment coverage is just 41%. These examples, com bined with the irregularities introduced by demography, underscore the limited utility of the IMR criterion in sub-Saharan Africa. For countries with an IMR already less than 1, the appearance of success even in the face of unacceptably high incidence could dampen the sense of urgency needed to forestall many new infections. From a financial perspective, the IMR could be useful for predicting national trends in the budgetary outlay required to treat people with HIV. From an epidemiological perspective, the IMR also approximates the effective reproductive number (RE), the average number of trans missions generated from a single infection. However, financial sustainability and RE are arguably both insuf ficient frameworks for epidemiological control. RE is com monly applied to ascertain whether transmission of an infectious disease will be perpetuated. At an RE threshold of less than 1, the epidemic will ultimately be eradicated. This metric is most appropriate for short-term infections, such as influenza and Ebola virus. Given the long duration of HIV infection, the delay between suppression of RE to less than 1 and elimination is commensurately protracted. New infections will continue to accrue throughout this timeframe. Transmission from even a small proportion of the existing 36∙7 million people with HIV6 results in many new infections year-on-year. As an illustration, consider a reduction of RE to 0∙9, at which elimination of the pandemic is eventually expected. In the next generation of transmission, a simple product of RE and the 36∙7 million people with HIV, would lead to 33∙0 million new infections. In the subsequent transmission generation, a further 29∙7 million infections would be anticipated, and 26∙7 million infections in the generation after that. Exacerbating the prolonged elimination phase, a lapse in intervention efforts at any point would cause a surge in growth of the epidemic.
Incidence-to-prevalence ratio In contrast to the IMR, the incidence-to-prevalence ratio (IPR) increases in response to high mortality among people with HIV; however, this ratio has its own potential problems. First, the value for the IPR that would
www.thelancet.com/hiv Published online October 9, 2018 http://dx.doi.org/10.1016/ S2352-3018(18)30178-4
Viewpoint
ubiquitously correspond to control is not clear. For a lifelong infection such as HIV, prevalence rises as life expectancy increases. As the life expectancy for an uninfected person can vary substantially across nations, an IPR indicative of low incidence in one context might translate to an unacceptably high incidence in another setting. Second, given that the denominator is an indication of the years lived with HIV, the IPR could be reduced either by an increase in life expectancy among people with HIV, or a drop in the average age at which infection is acquired. A reduction in the average age at which infection is acquired is both troubling and probable, given that the sub-Saharan African youth bulge is likely to reduce the average age of infection over the next decade, even as rates of HIV acquisition drop. As with the IMR, interpretation of the IPR would thus require disentangling the effects of demography and transmission, which diminishes the utility of the metric as a criterion for epidemic control.
Incidence-based criteria Incidence-based criteria would circumvent the short comings of the IMR and the IPR and have several advantages. First, these criteria are unaffected by fluctuations in mortality rates in people with HIV, whether driven by trajectories of impending HIV mortality or from less foreseeable events such as natural disasters or civil unrest that disrupt infrastructure of the health-care systems. Second, although the other proposed criteria require robust measures of multiple variables, milestones based directly on current incidence minimise empirical uncertainty. Thirdly, whereas incidence metrics have a straightforward meaning worldwide, the value of a ratio or proportion does not convey a sense of the magnitude of the public health problem. Incidence-based criteria would also be consistent with WHO’s definition for control of mother-to-child transmission of HIV.7 We support defining HIV control as incidence less than one in 10 000 people per year. This incidence metric is concordant with the standard used by WHO to define control for other diseases.8 Temporal milestones could include a reduction to one in 1000 by 2030, and to one in 10 000 by 2035. In practice, these targets often align with the 90% based reductions in incidence recommended by UNAIDS.4 For example, the 2030 milestone would represent a 91∙3% drop from the current 11∙5 per 1000 capita incidence in South Africa.6 As the impending youth bulge drives population growth, a steady national incidence rate could translate to a rising case count. However, absolute case counts require the context of population size for interpretation of risk, making the incidence rate a more comprehensive metric of control across settings.
Conclusion An appropriate definition of control for national HIV epidemics is essential to galvanise programme scale-up
and to optimise the implementation of interventions. Control criteria should have applicability to every country worldwide, particularly to those areas that are hardest hit, such as South Africa. Vigilance will be important to achieving these control targets, and should be maintained even after they are fulfilled. Sustainable control will require long-term investment in programmes ensuring access to early diagnosis, rapid transition into care, and lifetime support for an individual’s management of HIV. For any country-wide criteria, it should be acknowledged that national averages could hide worrisome trends at a cally or within more granular scale, either geographi high-risk groups. Efficiently achieving a low national incidence will undoubtedly involve targeted interventions within high-risk groups who might also be less likely to access services. Outreach to high-risk groups will be instrumental in effective treatment-as-prevention approaches and will ensure that control is steadily achieved at subpopulation levels and for the country overall. Despite the challenges still to be overcome to achieve worldwide control of HIV by any criteria, global financial assistance for the fight against HIV has fallen by more than 24% since 2012.9 Comprehensive control criteria can facilitate communi cation regarding the shortfall between available and required resources, guiding decision makers in the drive towards HIV control and, ultimately, elimination. Contributors APG conceptualised and drafted the Viewpoint and interpreted results. AP programmed the model and generated and interpreted the results. MCF contributed to writing, interpreted the results, drafted the response to reviewers’ comments, and did the literature search. JM programmed the model and interpreted the results. GEG contributed to writing. Declaration of interests We declare no competing interests. Acknowledgments The authors gratefully acknowledge funding from the National Institutes of Health (U01 GM15627 and U01 GM087719 for APG and AP; and 4T32AI007524-19 for MCF) and the Notsew Orm Sands Foundation (for APG, AP, and MCF). APG is also grateful for support from the Burnett and Stender Families Endowed Chair. The funders had no role in study design; in the collection, analysis, or interpretation of data; in the writing of the report; or in the decision to submit the paper for publication. References 1 UNAIDS. Ending AIDS: progress towards the 90–90–90 targets. 2017. http://www.unaids.org/sites/default/files/media_asset/ Global_AIDS_update_2017_en.pdf (accessed Jan 12, 2018). 2 UNAIDS. Making the end of AIDS real: consensus building around what we mean by ‘epidemic control’. 2017. http://www.unaids.org/ sites/default/files/media_asset/glion_oct2017_meeting_report_en. pdf (accessed Feb 5, 2018). 3 Medlock J, Pandey A, Parpia AS, Tang A, Skrip LA, Galvani AP. Effectiveness of UNAIDS targets and HIV vaccination across 127 countries. Proc Natl Acad Sci USA 2017; 114: 4017–22. 4 UNAIDS. Fast track: ending the AIDS epidemic by 2030. 2014. http://www.unaids.org/sites/default/files/media_asset/JC2686_ WAD2014report_en.pdf (accessed March 30, 2017). 5 PopulationPyramid. Population pyramids of the world from 1950 to 2100. 2017. https://www.populationpyramid.net/sub-saharanafrica/2017 (accessed June 6, 2018). 6 UNAIDS. AIDSinfo. 2016. http://aidsinfo.unaids.org/ (accessed June 28, 2016).
www.thelancet.com/hiv Published online October 9, 2018 http://dx.doi.org/10.1016/ S2352-3018(18)30178-4
3
Viewpoint
7
8
4
WHO. Criteria and processes for validation: elimination of mother-to-child transmission of HIV and syphilis. 2014. http://apps. who.int/iris/bitstream/handle/10665/112858/9789241505888_eng.pdf;j sessionid=816397988645AD6AD6961F995158A4E0?sequence=1 (accessed Jan 12, 2018). WHO. Accelerating work to overcome the global impact of neglected tropical diseases. 2012. http://apps.who.int/iris/bitstream/handle/ 10665/70809/WHO_HTM_NTD_2012.1_eng.pdf?sequence=1 (accessed March 30, 2017).
9
Global Burden of Disease Health Financing Collaborator Network. Spending on health and HIV/AIDS: domestic health spending and development assistance in 188 countries, 1995–2015. Lancet 2018; 391: 1799–829.
© 2018 Elsevier Ltd. All rights reserved.
www.thelancet.com/hiv Published online October 9, 2018 http://dx.doi.org/10.1016/ S2352-3018(18)30178-4