Just in the last two months, cases of paralysis caused by mutant vaccine viruses have been reported in the Philippines, Zambia, Togo and Chad. Because paralysis occurs in only about one in every 200 cases of polio, experts assume many more children have been infected. The latter contains weakened viruses that normally cannot cause disease but provide better protection than killed viruses. The strain that the Global Certification Commission for the Eradication of Poliovirus declared eliminated this week is Type 3 wild polio virus, the last case of which was seen in Nigeria in 2012. Type 1, the only wild strain left, circulates only in Pakistan and Afghanistan.

Source: New York Times October 23, 2019 22:00 UTC