than 150 countries have begun switching to a different polio vaccine - an important milestone towards polio eradication, health campaigners say.
The new vaccine will target the two remaining strains of the virus under a switchover 18 months in the planning.
There were just 74 cases of the paralysing disease in 2015 and there have been 10 so far this year.
All of the cases were in Afghanistan and Pakistan. Africa has been free of polio for more than a year.
Switching the vaccine from one successfully used to fight polio for more than 30 years is a huge logistical exercise.