Detection of Sabin-like type 2 poliovirus after global cessation of trivalent oral poliovirus vaccine in Hyderabad and Ahmedabad, India, August–September 2016

During 2 September–4 October 2016, 4 sewage samples collected in Hyderabad in Telangana state between 3 August and 19 September 2016 and 1 sewage sample collected in Ahmedabad in Gujarat state on 30 August 2016 tested positive for Sabin-like type 2 polioviruses. These polioviruses were detected more than 4 months after 25 April 2016 when India officially ceased use of trivalent oral poliovirus vaccine (tOPV) and switched to bivalent OPV (bOPV). The 4-month time interval between the date of the switch from tOPV (which contains Sabin attenuated type 1, 2, and 3 polioviruses), to bOPV (which contains Sabin attenuated type 1 and 3 polioviruses) and the detection of Sabin-like type 2 poliovirus suggests that tOPV use may have continued after global cessation, thus risking the creation of new type 2 vaccine-derived polioviruses (VDPV2s) which can cause paralytic poliomyelitis. Compared with the Sabin type 2 polioviruses found in tOPV, genetic sequencing of the Hyderabad poliovirus isolates showed zero, 1, 2 and 4 nucleotide changes in the VP1 region; sequencing of the Ahmedabad isolate showed 1 nucleotide change. These findings indicate that the isolated polioviruses had not replicated sufficiently to accumulate more than a few mutations to become VDPV2s and therefore the originating tOPV had likely been used within the previous 4 months.