Janne’s PhD thesis consisted of mathematical modelling studies comparing the potential benefit and cost-effectiveness of routine viral load monitoring of ART in sub-Saharan Africa. The main task was to develop a mathematical model for disease progression of HIV under ART. The model was used to compare the potential transmission from patients on ART with or without routine viral load monitoring, and to explore if the large observed differences in mortality between IeDEA-SA sites with and without viral load monitoring could be attributed to the monitoring strategy. The cost-effectiveness of viral load, CD4 and clinical monitoring were also compared. The results showed that routine viral load monitoring is very likely a cost-effective intervention, but mainly due to its indirect benefits, such as the ability to detect poor adherence and prevent treatment failures. Routine viral load monitoring is also expected to prevent about one third of HIV transmissions caused by treated patients. The PhD project included also other collaborative studies: a statistical analysis of first-year mortality and loss to follow-up in the entire Malawian national ART database, and three systematic reviews of pre-ART retention among adults, children, and pregnant women. Janne Estill continues to work at the ISPM as a postdoctoral researcher. He develops mathematical models and cost-effectiveness analyses for the disease progression and transmission for HIV, viral hepatitis and other infections, focusing in particular on the different patient management strategies of ART for HIV infected adults and children in sub-Saharan Africa.