"It is not a wild poliovirus outbreak. It is an outbreak of Sabin-Like Type 2 Derived (SLT2D). Similar outbreaks have been recently reported in Philippines, China, Indonesia, Nigeria, Democratic Republic of Congo and several other countries in Africa which have completely eradicated the poliovirus," Special Assistant to the Prime Minister on Health Zafar Mirza told Dawn news on Thursday.
There are three serotypes of wild poliovirus type 1, type 2, and type 3 each with a slightly different capsid protein.
Pakistan has been giving Type 1 and Type 3 viruses in Oral Polio Vaccines (OPVs), but had stopped administering Type 2 vaccine in 2014 and the virus could not be found even in environmental samples since 2016.
An environmental sample is declared positive if virus is found in sewage water.
"However, suddenly cases have been reported from different areas which mean there was some vial left in some laboratory or somewhere else and started spreading due to human error. Just after getting the cases, which cannot be included in the number of wild polio virus, we sent samples to the lab of Centres for Disease Control and Prevention (CDC), Atlanta, and after getting the confirmation, that children were paralysed due to Type 2 polio virus, we have started polio campaigns," Mirza said.
He said the virus had caused seven cases of paralysis in recent months, mainly in the northern parts of the country.
Meanwhile, the total number of polio cases reported in Pakistan so far this year is 72.
The World Health Organisation's Technical Advisory Group on Polio Eradication has said that Khyber Pakhtunkhwa is a major barrier to polio eradication efforts in Pakistan. It termed the situation caused by the parallel polio structure in the province 'crises', Dawn reported.
There are only two countries in the world, Pakistan and Afghanistan, where polio cases are still reported.
Pakistan remains under a polio-linked travel restriction imposed by the WHO due to which since 2014 every person travelling aboard has to carry a polio vaccination certificate.
( With inputs from IANS )