Trends and country-level variation in age at first sex in sub-Saharan Africa among birth cohorts entering adulthood between 1985 and 2020
Background: Debuting sexual intercourse is a life course event marking exposure to pregnancy or fatherhood, and sexually transmitted infections (STIs), including HIV. We systematically analysed the timing, distribution, and trends in age at first sex (AFS) in 42 sub-Saharan Africa (SSA) countries. Methods: We collated individual-level AFS data from nationally representative household surveys across SSA. We used a log-skew-logistic distribution to model the distribution of AFS in a Bayesian spatio-temporal hierarchical random-effect model to estimate national trends of AFS over time and space, adjusting for age at report biases. Findings: Small changes in AFS are observed between the birth cohorts entering adulthood between 1985 and 2020, ranging 0.79 years [-0.01-1.51] and 0.48 [-0.03-1.92] for female and male, respectively. Northern SSA countries show appreciable increase in AFS but its gender gap remains the widest compared with minimal gender gap in the southern countries. The gender gap shows little evidence of change over time in most of the countries. Female's AFS approach to a similar age across SSA while male's AFS varies between regions. Proportion ever had sex under fifteen and eighteen are as high 34% and 83%, respectively. AFS distribution is typically asymmetric with most of sexual debut events occur in a span of 3.9 [3.4-5.0] years. Female teen often reports higher AFS compare to their late twenties while male teen report lower AFS; both sexes tend to recall a higher AFS in older ages compared to their thirties. Interpretation: Women debut sexually earlier and in a shorter span of age than men. Northern and southern SSA gender gap are distinctively different. Since the ratifying of HIV/AIDS intervention programs in SSA, a stagnant trend in AFS had remained in the countries most affected by the epidemic.