Social capital mediates knowledge gaps in informing sexual and reproductive health behaviours across Africa.

Advancing sexual and reproductive health is essential for promoting human rights and women's empowerment, and combating the HIV/AIDS epidemic. A large body of literature across the social sciences emphasizes the importance of social capital, generated through the strength of social networks, for shaping health behaviours. However, large-scale measurement of social capital and social networks remains elusive, especially in the context of low-income countries. Here we delve into the role of social capital dynamics, and in particular social connectedness across communities as measured through Facebook friendship links, in shaping knowledge diffusion and behaviour related to sexual and reproductive health in 495 regions across 33 countries in Africa. Our findings demonstrate that regions with higher levels of social connectedness are more similar in their knowledge about contraception and HIV testing, as well as their adoption of these behaviours. We further observe that the influence of social connectedness becomes stronger when the knowledge gaps between regions are larger. In other words, regions are more similar in behaviours, despite knowledge gaps, when they are socially connected. These insights carry significant policy implications, especially for the design and targeting of public health campaigns. We highlight that social connectedness can serve both as a driver and an obstacle in behaviour formation, underscoring the importance of understanding its influence on health-related outcomes.