Background: Zimbabwe has made significant progress towards elimination of Mother to Child Transmission (MTCT) of HIV from 30% transmission rate in 2005 to 6.9% in 2016. However, in 2020 Harare province had a MTCT rate of 11.4% which was highest among all 10 provinces and was above the 5% national target. We determined the factors associated with vertical transmission of HIV in Harare City.

Methods: We conducted a 1:2 unmatched case control study where a case was defined as an HIV positive mother whose child was infected by 18 months of age. We interviewed 62 cases and 124 health facility controls. We collected data on prepartum, intrapartum, postpartum and service delivery factors using questionnaires, and health facility and patient records. Multivariate logistic regression analysis was performed to identify independent factors for MTCT.

Results: The median age was 27 (IQR 24-34) years for cases and 30.5 (IQR 25-36) years for controls. More controls (71.8%) had their maternal HIV diagnosis prepartum compared to cases (45.2%). Sixteen percent of cases had their diagnosis post-delivery compared to 0.8% of controls. Thirty-two (51.6%) baby cases had acquired HIV by 6 weeks postpartum. Prepartum maternal HIV diagnosis was protective [OR=0.32; 95% CI 0.17-0.61]. Independent factors associated with MTCT were non-adherence to ART [aOR 14.57; (2.18-97.44)], non-availability of infant ARV prophylaxis [aOR 14.91; (2.83-78.83)] and having a treatment partner [aOR 0.27; (0.11 - 0.68)].

Conclusions: MTCT was associated with late maternal HIV diagnosis and non-adherence to ART and interruptions to pediatric ART. Vertical transmission was high among babies whose mothers were diagnosed of HIV after conception and low among babies whose mothers had a treatment partner. This study highlights key intervention points in the acceleration of pediatric HIV elimination. We therefore recommend intensifying health promotion on prepartum testing for HIV, strengthening treatment support groups and adequate stocking of pediatric ARVs.