Changes in the live virus can cause paralysis, an extremely rare event. The virus infects one in every two hundred fifty million children who receive the oral vaccine. But researchers are working to prevent this tragedy from happening.

A man with polio in the village of Kosi in India

FAITH LAPIDUS: In general, the worldwide campaign against polio has made huge progress in the past twenty years. Polio vaccines have decreased the number of recorded cases by ninety-nine percent since nineteen eighty-eight. That was when the cooperative effort called the Global Polio Eradication Initiative began.

A vaccine is very important because antibiotic drugs do not help after someone is infected. Antibiotics can kill only bacteria, not viruses. There is no cure for polio. Care includes rest, fluids and medicines to control symptoms like high body temperature.

The wild polio virus passes freely from person to person. It spreads through fluids in the mouth and nose, waste material and water systems. The very rare vaccine-derived, or vaccine-linked, polio strikes when changes in genetic material affect the vaccine.

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BOB DOUGHTY: Polio is mainly a children’s disease. But adults also get it. Many people are infected without knowing it. They may have only a higher than normal temperature and pain in the throat. But when polio attacks the central nervous system, the person may not be able to stand or walk. When the disease affects breathing, a patient can die.