Background
A longstanding puzzle in efforts to control the spread of HIV, is why HIV treatment-as-prevention efforts in sub-Saharan Africa showed modest reductions in the occurrence of new infections despite achieving substantial gains in viral suppression.
Methods
Using data from a community-randomized trial of HIV prevention in sub-Saharan Africa we offer for the first time an evidence-based explanation of this longstanding puzzle. More specifically, we deep-sequenced whole genome HIV viral sequences from 5,114 trial participants in the 30-community BCPP (Botswana Combination Prevention Project) trial in Botswana to track the directional spread of HIV infections between communities. After, we combined the deep-sequenced HIV viral genome data with population census data to quantify the relative contribution of transmissions to intervention communities from individuals with HIV in the same community, other intervention communities, control communities, and (the vast majority of the country) non-study communities.
Results
We found that individuals with HIV in non-study communities accounted for most of the transmissions to trial communities 90% [81 – 93], and that the impact of the BCPP intervention in reducing transmissions to trial communities could have been considerably larger if the intervention had been applied nationwide 59% [3 – 87] compared to the observed 30% reduction.
Conclusions
This work transforms our thinking about the effectiveness of TasP for HIV prevention in general populations to a highly effective intervention when applied nationwide to maximize the capture of sources of transmission. We recommend that studies of infectious disease prevention consider the impact of sources of transmission beyond the reach of the intervention when designing and evaluating interventions to inform public health programs.