A mass polio immunisation campaign is starting in Angola in a bid to vaccinate all children under five.
The campaign is part of a series of programmes aimed at stopping a polio outbreak that has paralysed 24 children this year alone.
Over 7m vaccine doses are set to be delivered.
The World Health Organisation (WHO) says previous attempts to stop the virus circulating failed because too few children were vaccinated.
This outbreak in Angola started in 2007 and the WHO now considers it the greatest risk to Africa's polio eradication efforts.
Polio is a highly infectious virus which mainly infects young children.
It is transmitted through contaminated food and water and once it enters the intestine it multiplies and can spread into the nervous system.
In the worst cases, polio causes paralysis which is often permanent.
Current vaccines are highly effective in protecting children against infection.
This outbreak, despite previous vaccination campaigns, has now spread to the Democratic Republic of Congo.
The WHO say there is a high risk of the virus spreading further still.
Earlier efforts to stop the virus from spreading were not good enough, according to the UN health agency with not enough children vaccinated.
The virus can only be stopped if all children receive the vaccine.
The WHO estimates that in some areas more than a third of at risk children have not been immunised.
Oliver Rosenbauer, spokesperson for the Global Polio Eradication Initiative at the WHO said: "Children across Angola, and indeed Africa, will continue to be paralysed by this awful virus, and it's completely needless because it could so easily be prevented.
"The outbreak of course also has international implications. It has already this year spread to DR Congo, and we know that a past outbreak in 2006 spread to Namibia as well."
"But the good news is that we know this outbreak could be stopped very rapidly.
"If these upcoming immunisation campaigns are effectively implemented, this outbreak can be stopped in its tracks even by the end of the year.
"Africa is on the verge of being polio-free - and it can be rapidly and realistically achieved. "
Easier to control
These setbacks in central Africa are in stark contrast to improvements elsewhere on the continent.
Nigeria - which is the only country in Africa to never have been polio free - has seen a 99% drop in cases.
The outbreak in Angola should be much easier to control than in Nigeria simply because there are fewer children to vaccinate.
Another immunisation campaign is planned for the end of the month.