Eradicating Polio is still our number one priority
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~ Dr. Mary T. Bassett, NY Health Commissioner
How poliovirus spreads
Polio spreads between people when the virus enters the mouth, typically through hands contaminated with the stool of an infected person. The virus often spreads unnoticed because 70% of people infected do not show symptoms. About 25% of those infected develop mild symptoms similar to the flu.
One in 100 people infected develop severe disease such as permanent paralysis. Polio is fatal in 2% to 10% of people suffering from paralysis because the muscles used to breathe are immobilized.
The chain of transmission that introduced polio to New York is thought to have originated from abroad in someone who received the oral polio vaccine. The oral vaccine uses a weakened form of the virus that still replicates. In rare cases, the virus used in the vaccine can mutate, become virulent and spread to others.
The U.S. stopped using the oral vaccine more than two decades ago. It now uses a vaccine administered as a shot in which the virus is inactivated, which means it does not replicate and mutate. While this vaccine is very effective at preventing disease, it does not block transmission of the virus.
The oral polio vaccine can block transmission of poliovirus that occurs in nature, but carries the risk that the strain used in the vaccine could mutate to become virulent and result in spread of what’s called vaccine-derived poliovirus.