People generally believe that their own future will be better than the one of comparable others. Robust evidence documents such unrealistic optimism in many domains of life. Here, we examine how unrealistic optimism may affect people’s risk assessments of COVID-19 infection as well as their attitudes regarding behaviours intended to protect against contagion. In two studies conducted in the USA (N=160) and UK (N=161), at different times during the pandemic, we show that participants considered the likelihood of contracting and carrying the infection lower for themselves and their close other compared to an acquaintance, while they considered the likelihood of engaging in protective behaviours higher for themselves and their close other than an acquaintance. The findings document unrealistic optimism in relation to COVID-19. Such biases are particularly critical in relation to infectious diseases, where underestimating the risk for both oneself and close others may reduce precautions and increase virus spreading.