Introduction: Following waves of evictions from their homes in May 2016, approximately 100 families from the Comoros were gathered at Place de la République in Mamoudzou (Mayotte, France). In this context, an epidemiological surveillance system was established to assess the health status of this population and detect the occurrence of unusual health events. Materials and Methods: The surveillance system relied on the daily collection and analysis of activity data from healthcare providers on site (consultations by physicians at the Mayotte Hospital Center, the Red Cross first-aid station, and outreach teams from Médecins du Monde). A verification of vaccination status for diphtheria-tetanus-polio-pertussis (DTP), measles-mumps-rubella (MMR), hepatitis B, BCG, and pneumococcal (PnC) vaccines was conducted among children under 17 years of age, for whom catch-up vaccination was offered. Results: In total, between May 27 and June 22, 2016, 283 consultations were reported by various healthcare providers; 73% of these consultations involved children under 15 years of age. Among the 178 diagnoses reported by physicians at the Mayotte Hospital Center, 78% involved an infectious disease: 35% acute gastroenteritis, 25% upper respiratory tract infection, 8% a skin condition, 6% lower respiratory tract infection, and 3% another infectious disease. Among the 80 children whose vaccination status could be verified, only 30% were up to date on all five vaccines. Conclusion: The surveillance system made it possible to monitor the health status of this evolving population, characterized by the presence of a majority of young children. The extremely precarious living conditions in which these children lived left them vulnerable and exposed to epidemic risk. Despite a catch-up vaccination campaign, only two-thirds of the children still present at the end of the period benefited from this catch-up.