Background An immunization campaign using a two-dose regimen of Shanchol™ oral cholera vaccine (OCV) was implemented in the six most vulnerable neighborhoods of Nampula city, Mozambique. Of the 1292 suspected cholera cases reported in the city from September 2015 to July 2016, 66% of them originated in these six neighborhoods. The campaign’s objective was to prevent the emergence of a new cholera season, which usually starts between January and March [1].The campaign targeted 193,403 persons aged one year. Passive, health center-based assessment of adverse events following OCV immunization An AEFI is defined by the World Health Organization (WHO) as a medical occurrence following immunization that does not necessarily have a causal relationship with the usage of the vaccine [2]. Based on WHO guidelines, we implemented a surveillance system that began on the first day of vaccination and continued until 14 days after the second round [2]. The surveillance was carried out passively and based at the health facility, with voluntary presentation and reporting by vaccinated persons. The Acknowledgements We are grateful to the Provincial Health Direction of Nampula and the clinical teams at the health facilities. We would like to thank Marcello Gelormini and Egas Portugal for their support in the implementation of the surveillance. We also thank Lorenzo Pezzoli, Bradford D. Gessner and Martin Mengel for their guidance, and Deborah Azar and Claire MacDonald for proofreading. Funding The study was funded by Agence de Médecine Préventive, thanks to a charitable grant from the Bill & Melinda Gates Foundation, Seattle, WA.