We study the impact of exposure to COVID-19 on food security and diet diversity in four African countries (Uganda, Tanzania, Sierra Leone and Mozambique), using phone-based survey data collected throughout 2021. We find that in 2021, one in two households faced moderate-to-severe food insecurity and one in three households had borderline to poor diet diversity score. Food insecurity and poor diet diversity are particularly pronounced among certain groups of households, who characterize with large family sizes, low access to public services, own fewer assets, and mostly have a female, younger, and less educated person as household head. Both food insecurity and poor diet diversity are positively associated with exposure to COVID-19 – either through individual experience of having a virus or having people in their surroundings who had the virus. We show that tighter movement restrictions and a more drastic decline in household income in COVID-19-exposed areas were the main reasons for worsened food insecurity and poorer diet diversity. Vulnerable households rarely received financial support from governments, forcing many of them to use harmful food- related coping strategies and to borrow from other households.