The latter - it is attenuated virus from the live oral vaccine that has reverted to a form causing paralysis. Both forms of the polio vaccine are still effectiv

The latter - it is attenuated virus from the live oral vaccine that has reverted to a form causing paralysis. Both forms of the polio vaccine are still effective against it. <s>Why worry? Poliomyelitis is mild, most cases are asymptomatic, only one in 200 cases result in paralysis, and fatality rates are even lower.</s>