This dissertation seeks to contribute to the literature on the effects of health crises on the informal sector. The work examines the effects of the Covid-19 pandemic on the trade of street vendors in the city of Saint-Louis. Using descriptive analysis based on survey data, we observed that both the pandemic and the containment measures led to a decline in the activity and income of street vendors. Furthermore, the results of the empirical analysis carried out using the probit model revealed that the closure of markets had a negative and significant effect on merchants' income. Also, it appeared that variation in activity had a positive and significant effect on variation in income. On the other hand, we found that social assistance had a positive but insignificant effect on income variation. Overall, the study showed that the drop in activity induced by the containment measures, notably the closure of markets, increases the vulnerability of street vendors in terms of a drop in income.