Getting to under 1% vertical HIV transmission: lessons from a breastfeeding cohort in South Africa.

We report here on the transmission of HIV in a cohort of breastfeeding infants enrolled in a prevention of mother to child HIV transmission (PMTCT) programme at the epicentre of the HIV pandemic. South Africa implemented option B+ for PMTCT in 2015. Between 2013 and 2018, we enrolled 1219 infants born to HIV positive women into a non-inferiority trial assessing the current cotrimoxazole prophylaxis guidelines for HIV-exposed uninfected infants. Breastfeeding mothers and infants were enrolled and followed up at one of two clinics in eThekwini, KwaZulu-Natal, until 12 months of age. During the study period, 8 infants seroconverted (<1% transmission); these were likely four birth transmissions and four breastfeeding transmissions. It is critical in the post option B era to assess the reasons for vertical transmission of HIV to enable healthcare workers and policy makers to provide strategies to mitigate future infections. This report details the possible contributors to vertical transmission in this cohort and highlights the continued strategies that should be employed to further our goal towards reaching the elimination of mother to child HIV transmission.