Improving estimates of children living with HIV from the Spectrum AIDS Impact Model

Abstract

Objective: Estimated numbers of children living with HIV determine programmatic and treatment needs. We explain the changes made to the UNAIDS estimates between 2015 and 2016, and describe the challenges around these estimates.

Methods: Estimates of children newly infected, living with HIV, and dying of AIDS are developed by country teams using Spectrum software. Spectrum files are available for 160 countries, which represent 98% of the global population. In 2016, the methods were updated to reflect the latest evidence on mother-to-child HIV transmission and improved assumptions on the age children initiate antiretroviral therapy. We report updated results using the 2016 model and validate these estimates against mother-to-child transmission rates and HIV prevalence from population-based surveys for the survey year.

Results: The revised 2016 model estimates 27% fewer children living with HIV in 2014 than the 2015 model, primarily due to changes in the probability of mother-to-child transmission among women with incident HIV during pregnancy. The revised estimates were consistent with population-based surveys of HIV transmission and HIV prevalence among children aged 5-9 years, but were lower than surveys among children aged 10-14 years.

Conclusions: The revised 2016 model is an improvement on previous models. Paediatric HIV models will continue to evolve as further improvements are made to the assumptions. Commodities forecasting and programme planning rely on these estimates, and increasing accuracy will be critical to enable effective scale-up and optimal use of resources. Efforts are needed to improve empirical measures of HIV prevalence, incidence, and mortality among children.

Figure 1. Pediatric HIV calculations in Spectrum AIDS Impact Module

Rectangular boxes are assumptions and pre-populated data included in the Spectrum software. Rounded rectangular boxes are data that countries enter and update every year. Diamonds reflect calculations.

Figure 2. Probability of HIV transmission by PMTCT regimen

Peripartum transmission is the probabilty of transmitting between a mother and child during the pregnancy and delivery. Postpartum transmission is a monthly probability that is multiplied by the expected duration of breastfeeding which varies for women wihtin the PMTCT programme and women not in the programme who are not likely to know their HIV status. The probability of transmission to the infant among women who are infected while breastfeeeding is a one-time risk and is 27% (compared to 28% in the 2015 model). The sources for the 2015 model assumptions are Rollins et al 2012, except for ART started during pregnancy which was updated after the Rollins et al paper. The 2016 model assumptions are previously published in an unpublished report by Lynne Mofenson.

Figure 3. The number of children living with HIV, new HIV infections among children, and AIDS-related deaths among children in the 2015 model versus 2016 model

Estimates for 2015 are not available from the 2015 model because surveillance and programme data were not yet available at the time the country developed the file in early 2015. Uncertainty bounds are available for the 2016 model. They are excluded from the figures to simplify the presentation of the figure.

Figure 4

Mother to child transmission rates at age six weeks and final (after breastfeeding) rates based on studies from South Africa [15] and Zimbabwe [16] compared to the 2016 model results. In the South African study the MTCT rate was measured at 8 weeks, while the modelled estimate is for approximately 6 weeks. In the Zimbabwe study the MTCT rate was measured at 9–18 months, while the final modelled transmission rate is estimated at 36 months.

Figure 5. HIV prevalence among children 5–9 and 10–14 years

HIV prevalence rates from the models are for the same year as the survey was implemented (the year is listed next to the country name). For example the prevalence rates from the Kenya AIDS indicator Survey are all for the year 2012. Sources: Kenya AIDS Impact Survey 2012, Mozambique AIDS Indicator Survey 2009, Swaziland Demographic and Health Survey 2006, South African HIV Prevalence and Incidence Survey, Botswana AIDS Impact Survey 2012. [–21]