Update on Vaccine-Derived Poliovirus Outbreaks…

Detection of cVDPV2

During January 2020–June 2021, there were 38 cVDPV2 emergences in active transmission in 34 countries; 28 (82%) of these countries are in Africa (Table) (Figure 1). Nineteen (50%) of the 38 emergences were previously detected during 2017–2019, three (8%) (ETH-ORO-4, ETH-SOU-2, and NIE-SOS-7) were newly detected in 2019 but were confirmed after the last global report, and 16 (42%) were newly detected during 2020–2021 (1,3). During the reporting period, fifteen (58%) of the 26 emergences in active transmission in African countries were detected, either in AFP patients or through environmental surveillance, outside of the country of first isolation of genetically linked virus (Figure 2). No polioviruses genetically linked to two previously described emergences (CHN-XIN-1 and ZAM-LUA-1) have been detected since 2019 (1,3).

Western Africa. The previously described cVDPV2 emergence (NIE-JIS-1) (1,3), first detected in Nigeria in 2018, continued to circulate during the reporting period. Since first detected, genetically linked virus has circulated in 17 west and central African countries, from Mauritania to Cameroon; during the reporting period; circulation was documented in 16 of the 17 countries (excluding Cameroon) resulting in 310 cases of cVDPV2 in 14 countries and detection through environmental surveillance in 13 countries (1,3). The most recent detection of the previously described NIE-KGS-1 emergence was through environmental surveillance in January 2020 (1,3).

During July–September 2019, the NIE-SOS-7 emergence was detected through environmental surveillance in Nigeria; circulation was confirmed after the previous global update (3). Virus genetically linked to the NIE-SOS-7 emergence was detected in specimens from AFP patients and from one healthy child in Mali during 2020. NIE-SOS-7 was not detected in Nigeria during 2020; however, genetically linked virus was isolated in 2021 from specimens obtained from AFP patients and healthy children, and through environmental surveillance. Two new cVDPV2 emergences (NIE-SOS-8 and NIE-ZAS-1) were detected and circulated in Nigeria during the reporting period, with the most recent detections in September 2020 and June 2021, respectively. During June 2021, NIE-ZAS-1 emergence was detected in Niger. There was no evidence of continued circulation of any other previously described emergences first detected in Nigeria (1,3). The previously reported TOG-SAV-1 cVDPV2 emergence circulated in Burkina Faso, Côte d’Ivoire, and Togo during the reporting period (3).

Central Africa. The most recent detection of the ANG-HUI-1 emergence in Angola was in February 2020; however, genetically linked virus was isolated from specimens collected from AFP patients and one healthy child during late 2020 in the Republic of the Congo (1,3). The ANG-LUA-1 emergence was most recently detected in the Democratic Republic of the Congo and Angola in specimens from AFP patients with paralysis onset in January and February 2020, respectively and in a healthy child in the Republic of the Congo in October 2020 (3). The ANG-LNO-2 emergence was last detected in Angola in December 2019; the most recent isolation of genetically linked virus was in the Democratic Republic of the Congo from specimens from an AFP patient with paralysis onset in February 2020 (1,3). No polioviruses genetically linked to two previously described emergences (ANG-LNO-1 and ANG-MOX-1) were detected during the reporting period (1,3).

The CHA-NDJ-1 emergence was first detected in Chad and then Cameroon during 2019; genetically linked virus was detected during the reporting period in Cameroon, the Central African Republic, Chad, Egypt, Ethiopia, South Sudan, Sudan, and Uganda (3). Genetically linked virus was most recently detected in Egypt and Uganda through environmental surveillance during June 2021. This emergence resulted in 204 paralytic cases in five of these eight countries during the reporting period.

Of the seven emergences first detected in the Central African Republic during 2019 (CAR-BAM-1, CAR-BAM-2, CAR-BER-1, CAR-BIM-1, CAR-BIM-2, CAR-BIM-3, and CAR-BNG-1), three (CAR-BER-1, CAR-BIM-3, and CAR-BNG-1) continued to circulate and spread internationally during the reporting period (1,3). Virus genetically linked to CAR-BER-1 was detected in Cameroon, the Central African Republic, and the Republic of the Congo; to CAR-BIM-3 was detected in Chad; and to CAR-BNG-1 was detected in Cameroon, the Central African Republic, the Republic of the Congo, and the Democratic Republic of the Congo.

Two previously described emergences (DRC-KAS-1 and DRC-KAS-3) detected in the Democratic Republic of the Congo in 2019 continued to circulate (1,3). After being first detected in 2019 in specimens from an AFP patient and healthy children (1), the DRC-KAS-1 emergence was not detected again until early 2021 in the Republic of the Congo in the specimens from an AFP patient. During the current reporting period, the DRC-KAS-3 emergence resulted in 82 paralytic cases in the Democratic Republic of the Congo, with the most recent paralysis onset in April 2021. Three new emergences (DRC-EQT-1, DRC-MAN-2, and DRC-TPA-2) were detected during the reporting period. There was no evidence of continued circulation of any other previously described emergences first detected in the Democratic Republic of the Congo (1,3).

Horn of Africa. The previously described SOM-BAN-1 emergence continued to circulate during the reporting period; genetically linked virus was detected each year during 2017–2021 in Somalia, and during 2018 and 2020–2021 in neighboring Kenya (1,3). During 2020, a new emergence (SOM-AWL-1) resulted in one case in Somalia and two cases in Ethiopia. Three previously described cVDPV2 emergences (ETH-ORO-1, ETH-ORO-2, and ETH-ORO-3) detected in Ethiopia in 2019 were detected during the reporting period in Ethiopia and Somalia (3). Two new emergences (ETH-ORO-4 and ETH-SOU-2) were confirmed after the previous global update (3) and subsequently resulted in six paralytic cases in Ethiopia. During 2020–2021, an additional new emergence (ETH-SOU-1) that circulated in Ethiopia and South Sudan resulted in ten paralytic cases. There have been no detections of the previously described ETH-SOM-1 emergence since 2019 (3).

Afghanistan, Iran, Pakistan, and Tajikistan. Among the five previously described cVDPV2 emergences detected in 2019 in Pakistan (PAK-GB-1, PAK-GB-2, PAK-GB-3, PAK-KOH-1, and PAK-TOR-1) only PAK-GB-1 and PAK-TOR-1 continued to be detected during the reporting period (3). The latest detection of PAK-TOR-1 was in a healthy child in Pakistan in early 2020. During the reporting period, PAK-GB-1 spread internationally resulting in a total of 251 cases in Afghanistan and Tajikistan, and 114 cases in Pakistan. There have been 11 environmental surveillance isolations of PAK-GB-1 in Iran, but no paralytic cases. During the reporting period, seven cVDPV2 emergences (PAK-FSD-1, PAK-FSD-2, PAK-KAM-1, PAK-KHI-2, PAK-LKW-1, PAK-PWR-1, and PAK-ZHB-1) were newly detected in Pakistan resulting in 15 paralytic cases; two cVDPV2 emergences (AFG-HLD-1 and AFG-NGR-1) were newly detected in Afghanistan during 2020 and spread to Pakistan. An additional cVDPV2 emergence (PAK-PB-1) was first and most recently detected through environmental surveillance in Pakistan in December 2019; confirmation of circulation occurred after the last global report (3).

Malaysia and the Philippines. The most recent detection of the PHL-NCR-1 cVDPV2 emergence in the Philippines was in January 2020 (3). The most recent detection of this emergence globally was through environmental surveillance during February 2020 in Malaysia (3).