Environmental Isolation of Circulating Vaccine-Derived Poliovirus After Interruption of Wild Poliovirus Transmission — Nigeria, 2016

Abstract

In September 2015, more than 1 year after reporting its last wild poliovirus (WPV) case in July 2014 (1), Nigeria was removed from the list of countries with endemic poliovirus transmission,* leaving Afghanistan and Pakistan as the only remaining countries with endemic WPV. However, on April 29, 2016, a laboratory-confirmed, circulating vaccine-derived poliovirus type 2 (cVDPV2) isolate was reported from an environmental sample collected in March from a sewage effluent site in Maiduguri Municipal Council, Borno State, a security-compromised area in northeastern Nigeria. VDPVs are genetic variants of the vaccine viruses with the potential to cause paralysis and can circulate in areas with low population immunity. The Nigeria National Polio Emergency Operations Center initiated emergency response activities, including administration of at least 2 doses of oral poliovirus vaccine (OPV) to all children aged <5 years through mass campaigns; retroactive searches for missed cases of acute flaccid paralysis (AFP), and enhanced environmental surveillance. Approximately 1 million children were vaccinated in the first OPV round. Thirteen previously unreported AFP cases were identified. Enhanced environmental surveillance has not resulted in detection of additional VDPV isolates. The detection of persistent circulation of VDPV2 in Borno State highlights the low population immunity, surveillance limitations, and risk for international spread of cVDPVs associated with insurgency-related insecurity. Increasing vaccination coverage with additional targeted supplemental immunization activities and reestablishment of effective routine immunization activities in newly secured and difficult-to-reach areas in Borno is urgently needed.

Cessation of Trivalent Oral Poliovirus Vaccine and Introduction of Inactivated Poliovirus Vaccine — Worldwide, 2016

“…In April 2016, a cVDPV2 was identified in an environmental sample collected in March 2016 in northeastern Nigeria, before cessation of tOPV use, but genetic testing indicated that it is part of a known cVDPV2 lineage that was undetected after isolation from an environmental sample in early 2014 (9). Following the protocol for responding to detection of WPV2 after the switch and using the prepared mOPV2 stockpile, SIAs with mOPV2 were implemented in northeastern Nigeria after detection of the cVDPV2.…”

Polio endgame risks and the possibility of restarting the use of oral poliovirus vaccine

“…Table 1 categorizes the 44 independent serotype 2 VDPV (VDPV2) events detected in the 2 years since the tOPV-bOV switch in April-May 2016, based on our subjective interpretation of limited information [48,49,54,55]. Table 1 does not include at least 2 iVDPV2s detected before the switch that still excreted after the switch (1 in Iran and 1 in the United Kingdom) [48] or a breach in containment in the Netherlands in 2017 that resulted in a WPV2-infected laboratory worker [39].…”

“…Table 1 does not include at least 2 iVDPV2s detected before the switch that still excreted after the switch (1 in Iran and 1 in the United Kingdom) [48] or a breach in containment in the Netherlands in 2017 that resulted in a WPV2-infected laboratory worker [39]. Table 1 includes one cVDPV2 event officially notified days after OPV2 cessation that identified continued transmission of a persistent cVDPV2 outbreak in a sewage sample collected in the security-compromised state of Borno, Nigeria just prior to the switch [49]. All other events represent detections of cVDPV2s (7 events), iVDPV2s (9 events), or aVDPV2s (28 events) not identified prior to the switch.…”

“…April or May 2016, depending on country) b Through April, 2018 (note that Somalia,, Nigeria, and DRC reported cVDPV2 cases during mid-2018) c Includes one event representing a renewed detection (environmental sample collected in March, 2016, but cVDPV2 notified days after the switch) of a persistent transmission of a cVDPV2 last detected in 2014 [49] d Kenya detected the cVDPV2 from Somalia in an environmental sample collected in March, 2018 [54] e Unusually long chain for transmission differentiated from ‘normal’ excretion distribution using a cut-off of six months since last known homotypic OPV use f Unauthorized post-switch mOPV2 or tOPV use also possible based on circumstantial information g Insufficient information available to establish nature of this event…”

“… c Includes one event representing a renewed detection (environmental sample collected in March, 2016, but cVDPV2 notified days after the switch) of a persistent transmission of a cVDPV2 last detected in 2014 [49]…”