The following editorial appeared recently in The Washington Post.

The world witnessed only 223 polio cases last year, the lowest level in history and an impressive advance from the hundreds of thousands of children afflicted as recently as the 1980s. However, the eradication quest is not over, and the next steps look difficult. Wiping out a disease has been done only once before, with smallpox.

The Global Polio Eradication Initiative, an umbrella group, has unveiled a promising strategy over the next five years to reach zero cases, the elusive goal set a quarter-century ago.

The polio virus affects the nervous system and can lead to paralysis, largely among children age 5 and younger.

The virus is highly contagious, can spread rapidly and remains endemic in Pakistan, Afghanistan and Nigeria. In Pakistan, 15 health workers in the anti-polio campaign have been killed since July, and a World Health Organization official estimated that 240,000 children have missed vaccinations in the tribal areas because of security concerns. In Nigeria, nine workers have been killed this year.

Any effort to conquer polio is going to have to fully protect those carrying out the vaccination campaigns.

The task of complete eradication grows harder. The oral polio vaccine, which contains a live, weakened virus, has been key to the dramatic progress in reducing cases. But on very rare occasions, the virus strain in the oral vaccine has reverted to a paralytic one and begun to circulate.

The new global strategy involves a switch to an inactivated vaccine that can attack the circulating virus. This requires a shot, not just an oral drop. While the oral dose costs about 20 cents apiece, the inactivated one costs a dollar or more. The switch to the inactivated virus is an important firewall against a further outbreak, but it won't be easy.

The five-year strategy is estimated to cost $5.5 billion from varied sources, a partnership spearheaded by the WHO, Rotary International, the Centers for Disease Control and Prevention and UNICEF with support from the Bill & Melinda Gates Foundation.

Hopes for wiping out polio globally have been raised by the achievement of India, now free of the virus. But success is not assured and demands a fight to the finish.