Aid agencies are planning to immunise three million people in central Africa after a polio outbreak, which has killed more than 100 people.
Hundreds more have been paralysed by the disease, authorities have said.
The disease broke out in Congo-Brazzaville, but has also affected parts of neighbouring Democratic Republic of Congo and Angola.
The government said the vast majority of deaths had occurred in the city of Pointe-Noire in Congo-Brazzaville.
Congo-Brazzaville had previously recorded its last case of indigenous polio in 2000.
The vaccination plan is being conducted by several aid agencies, including Unicef and the World Health Organization (WHO).
"The first round of a mass vaccination campaign targeting three million people will begin Friday, in response to a polio epidemic which has unusually claimed a majority of adult victims," said a joint statement.
The majority of reported cases and deaths had occurred in males aged over 15.
Polio, which damages the nervous system, causing paralysis and death if untreated, normally strikes young children.
The immunisation plan will start in Pointe-Noire, the epicentre of the outbreak, and extend to surrounding areas.
"Every man, every woman, every child will be immunised irrespective of their past immunisation status," said Dr Luis G Sambo, WHO's regional director for Africa.
"This way we can be assured that everybody is reached, including young adults, whose immunity may be low."
Congo's director general of health, Alexis Elira Dokekias, said the victims had either not been sufficiently immunised or not immunised at all.
Reports say women and girls may have developed some immunity to the disease through contact with babies that had been immunised.
In 2000 and 2001, the Congo, the Democratic Republic of Congo, Angola and Gabon carried out synchronised campaigns against the polio virus.