The 1,046 people were travelling in seven boats from Gambia to the Canary Islands before they became stranded at sea, the organisation said on Monday.
The boats were stopped in the last week of August, and the passengers have been taken to the cities of Nouadhibou in Mauritania and Rosso and Dakar in Senegal.
The survivors had suffered from extreme dehydration, unconsciousness, bone fractures, extreme fatigue and skin, stomach and respiratory infections, according to MSF, which has provided emergency medical assistance.
Most of those on board were from Senegal and Gambia. Others were from Mali, Guinea and Ivory Coast, among others.
