A team from the World Health Organisation is investigating how an 11-month-old infant has been infected with polio virus in Maharashtra’s Beed district, in spite of stringent efforts by the Health Ministry to control its spread.

It is for the first time since March 2012 that the State has registered a polio case. Health Minister Suresh Shetty told The Hindu that he had ordered an investigation and would get the WHO report on Saturday morning.

The infant, hailing from Kanhapur village in Dharur tehsil, has been found to have the Vaccine Derived Polio Virus (VDPV) type 2, a rare strain which is genetically mutated from the strain contained in the oral polio vaccine.

The infant was initially admitted to the government medical college in Ambejogai, Beed, on May 3. “The child had high fever and suffered paralysis in all four limbs,” said A.K. Singare, residential medical office of Swami Ramanand Teerth Hospital, Ambejogai. The child was then transferred to the Latur government medical college on May 16 and it tested positive for VDPV on June 1.

VDPVs are further classified into circulating vaccine-derived poliovirus, immunodeficiency-related vaccine-derived poliovirus (iVDPV) and ambiguous vaccine-derived poliovirus. It is still unclear which form of the virus has infected the child.

Officials in charge of the case said the child having been ill for prolonged periods indicated the possibility of iVDPV, which could be further linked to lack of sanitation and health facilities.

Though the case has rung alarm bells, health experts say this does not threaten India’s polio-free status. Detecting VDPV is part of the surveillance system but only infections caused by wild polio virus strains like P1 and P3 are counted while declaring a country polio-free, and not a P2 strain which is caused by the oral polio vaccine and hence causes VDPV infection.

India’s last case of wild polio infection was reported on January 13, 2011 from West Bengal.

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