Short answers, pulled from the story.
About one to five in 1,000 cases of poliovirus infection progress to paralytic disease. Approximately 72 percent of infections produce no symptoms at all, and another 24 percent cause only mild, temporary illness such as sore throat and fever.
Jonas Salk developed the first successful polio vaccine at the University of Pittsburgh, using chemically inactivated poliovirus grown in monkey kidney tissue. It was announced to the world on the 12th of April 1955.
Post-polio syndrome is a slow, progressive condition that affects between 25 and 50 percent of people who recovered from paralytic polio in childhood. It produces new muscle weakness and extreme fatigue decades after the original infection, thought to result from the eventual failure of the enlarged motor neurons that compensated during recovery. There is no specific treatment.
In 2022, there were 30 confirmed wild poliovirus type 1 cases worldwide, with two in Pakistan and 20 in Afghanistan, plus eight in Mozambique - the first cases there since 1992. All were caused by a strain of Pakistani origin.
Afghanistan and Pakistan are the only two countries where wild poliovirus type 1 still circulates naturally. Wild poliovirus types 2 and 3 have been certified eradicated, in 2015 and 2019 respectively.
Vaccine-derived poliovirus (cVDPV) occurs when the weakened live virus in the oral polio vaccine spreads in communities with low vaccination coverage and mutates over successive transmissions, reverting to a form that can cause paralysis. By 2017, cases of vaccine-derived poliovirus outnumbered wild poliovirus cases for the first time. An improved oral vaccine with greater genetic stability, nOPV2, received full WHO licensure in December 2023 to address this risk.