The World Health Organization welcomed a "historic step" toward a polio-free world on Thursday as an expert panel certified that the second of three types of the crippling virus has been eradicated globally.

The announcement by the Global Commission for the Certification of Poliomyelitis Eradication says the type 3 poliovirus was wiped out this week. The achievement comes four years after type 2 was eradicated in 2015.

Type 1 still remains but is now circulating in Afghanistan and Pakistan only.

"The achievement of polio eradication will be a milestone for global health. Commitment from partners and countries, coupled with innovation, means of the three wild polio serotypes, only type one remains," said Dr. Tedros Adhanom Ghebreyesus, Director-General of the World Health Organization and Chair of the Global Polio Eradication Initiative (GPEI) Polio Oversight Board. "We remain fully committed to ensuring that all necessary resources are made available to eradicate all poliovirus strains. We urge all our other stakeholders and partners to also stay the course until final success is achieved," he added.

Globally, polio cases have fallen by 99.9%.  In Africa, Nigeria had its last case more than three years ago. It’s possible that Nigeria, and all of Africa, will be declared polio-free.

However, vaccine-derived polio is still prevalent in 12 countries: Angola, Benin, Cameroon, Central African Republic, Chad, Democratic Republic of the Congo, Ethiopia, Ghana, Niger, Nigeria, Togo and Zambia.

Cases of vaccine-derived polio can occur in places where immunity is low and sanitation is poor, as vaccinated people can excrete the virus, putting the unvaccinated at risk.

Polio eradication efforts have saved the world more than US$27 billion in health costs since 1988. A sustained polio-free world will generate further US$14 billion in savings by 2050, compared to the cost countries would incur for controlling the virus indefinitely.

Source: World Health Organization