The vaccination campaign started before the approval of the ethics committee was obtained. The study is therefore no longer of interest to be carried out.

A previous seroprevalence survey showed very high seroprevalence levels among residents of the two among the residents of the two migrant workers' hostels surveyed, indicating a high level of circulation of the virus SARS-COV-2 during the 1st wave of COVID-19. The constitution of a cohort after the event would be an opportunity to obtain opportunity to obtain answers to crucial questions: duration of immunity, potential reinfections potential reinfections, potential re-clustering. Going back to check the serological status seems feasible, especiallyespecially in the Foyers de Travailleurs Migrants (high probability of finding the participants).

There is an obvious scientific interest around the duration of immunity and reinfections in a population highly exposed during the first wave. Several articles document the decline of IgG antibodies in the months following an infection, but very few infection, but very few evaluate the protective character in the medium term (>=6 months), especially in asymptomatic individuals. We are also concerned about the circulation of We are also concerned about the circulation of new variants and the immunity acquired after infection in residents.

To date, no study on the duration of immunity has been conducted in migrant worker's residences.

Inclusion Criteria:

• All individuals who consented to participate in the 1st study and who consent to participate in this study
• All individuals 18 years of age or older not residing in the 2 MWRs in July 2020 and permanently living in the MWR since September 2020 who consent to participate in this study

Exclusion Criteria:

• Unwillingness to provide informed consent
• Unwillingness to provide blood
• Contraindication to venepuncture

residents of 2 Migrant Workers

The research team will develop a range of activities to disseminate the study findings. These dissemination activities will be coordinated by MSF and Epicentre. The results will be presented in an internal report and an external report for the Ministry of Health (MoH), the French National Public Health Agency and Institute Pasteur.

An abstract of the findings will be submitted for presentation at a scientific conference, and at least one manuscript will be submitted for publication in a peer-reviewed scientific journal.

The findings of the survey will also be used for advocacy purposes, in coordination with community leaders of participating communities.

The results of the survey (lay version of the report), and their possible use for advocacy / communication, will be shared with the staff, resident representatives and residents of the MWRs, whether or not they actually participated in the study.