Table 1.
Categories of serotype 2 vaccine-derived poliovirus (VDPV2) events detected since the tOPV-bOPV switch and as of April, 2018, based on our subjective interpretation from limited information [48,49,54,55].
| Category | Most likely source | Number of events detected in |
Countries that detected the virus (number of independent events in country if not 1) | Number of AFP casesb | ||
|---|---|---|---|---|---|---|
| 2016a | 2017 | 2018b | ||||
| cVDPV2 | Pre-switch tOPV use | 3c | 3 | 0 | Nigeria (2), Pakistan, Democratic Republic of the Congo (DRC), Syria, Somalia, Kenya (0)d | 99 |
| Unauthorized post-switch tOPV use | 0 | 1 | 0 | DRC | 2 | |
| Post-switch authorized mOPV2 use | 0 | 0 | 1 | Nigeria | 0 | |
| iVDPV2 | Pre-switch tOPV use | 6 | 3 | 0 | Nigeria, Argentina, Egypt (3), West Bank and Gaza, Pakistan, Iran, Israel | 5 |
| aVDPV2, tail of ‘normal’ excretion distribution from OPV recipients and close contactse | Pre-switch tOPV use | 8 | 0 | 0 | India (2), Yemen, Pakistan (3), Afghanistan, Somalia | 3 |
| Post-switch authorized mOPV2 use | 0 | 13 | 0 | Nigeria (9), Pakistan (4) | 0 | |
| aVDPV2, unusually long transmission chaine | Pre-switch tOPV use | 2 | 1 | 0 | Mozambique, Pakistan, India | 1 |
| Post-switch authorized mOPV2 use | 0 | 0 | 1f | Nigeria | 0 | |
| aVDPV2 in environment, likely from immunodeficient excretor | Pre-switch tOPV use | 0 | 1 | 0 | Australia | 0 |
| Other aVDPV2g | Pre-switch tOPV use | 1 | 0 | 0 | Russia | 0 |
Abbreviations: AFP, acute flaccid paralysis, aVDPV2, serotype 2 ambiguous vaccine-derived poliovirus; cVDPV2, serotype 2 circulating vaccine-derived poliovirus; DRC, Democratic Republic of the Congo; iVDPV2, serotype 2 immunodeficiency-associated vaccine-derived poliovirus; mOPV2, serotype 2 monovalent OPV; OPV, oral poliovirus vaccine, tOPV, trivalent OPV
a Post-switch only (i.e. 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