The Philippines declared an outbreak of polio on 19th September, after a 3-year-old girl from Lanao del Sur (on Mindanao island) was confirmed to have developed acute flaccid paralysis from vaccine-derived Type 2 poliovirus infection. A second case of polio due to the same virus was announced 2 days later, also on Mindanao but more than 700 km away from Lanao del Sur.
These cases are of significant interest because the World Health Organization (WHO) had withdrawn Type 2 poliovirus from the oral polio vaccine (OPV) in 2016, hence only the bivalent Type 1 and Type 3 poliovirus OPV has been available in Philippines from mid-2016. The implications are that both these children have been infected by a vaccine-derived Type 2 poliovirus that has been circulating in the wild for some time, and has mutated to the extent that it is able to cause disease – a phenomenon that occurs mainly in under-vaccinated and non-immune populations. A mass polio vaccination campaign has just been initiated in the Philippines.
Globally, wild-type polio cases have also been on the rise, with a marked increase in cases in Pakistan. Vaccine-derived polio cases have held steady at 80 cases 1 Jan 2019 to 18 Sep 2019.
Singapore has been certified free of polio since 2000, and the history of polio containment and eradication efforts leading to that point are concisely summarised in this 2012 article published in the Annals of the Academy of Medicine Singapore. The local immunisation schedule comprises 4 doses of inactivated polio vaccine (IPV) at age 3, 4, 5, and 18 months, followed by 1 dose of OPV at 10-11 years of age. Polio vaccination rates are generally above 96% in Singapore.