VDPV outbreaks were tabulated and mapped by country, serotype, source of detection, emergence group, and other characteristics. cVDPV emergences with ongoing transmission detected outside of the country of first isolation during 2024, either through AFP cases or ES, were also plotted. Descriptive analyses were conducted using R software (version 4.4.1; R Foundation). These activities were reviewed by CDC, deemed not research, and were conducted consistent with applicable federal law and CDC policy.§§
During January 2023-June 2024, a total of 74 cVDPV outbreaks were detected in 39 countries, with 672 confirmed AFP cases identified in 27 of the 39 countries (Figure 1) (Table). Twelve countries reported cVDPV circulation detected only through ES or sampling of healthy community members. Cocirculation of cVDPV1 and cVDPV2 was detected in two countries in the WHO African Region (Democratic Republic of the Congo [DRC] and Mozambique). During the reporting period, no new cVDPV3 emergences were detected. Overall, the number of cVDPV AFP cases declined from 881 in 2022 to 672 during January 2023-June 2024 (Supplementary Figure, https://stacks.cdc.gov/view/cdc/164302). Despite the decline in AFP case counts, the number of countries reporting AFP cases remained approximately the same. The number of cVDPV1 AFP cases declined substantially over the reporting period.
During January 2023-June 2024, cVDPV1 circulation was detected in three countries (DRC, Madagascar, and Mozambique) from four cVDPV1 emergences (Figure 1) (Table). No new countries or emergences were reported since 2022. A total of 140 AFP cases were confirmed, with 111 reported from DRC, 106 (75%) in 2023, and five (5%) in the first half of 2024. Recent cVDPV1 detections occurred in April 2024 in DRC (RDC-TAN-1) and May 2024 in Mozambique (MOZ-NPL-2). The latest cVDPV1 detection in Madagascar occurred in September 2023.
During January 2023-June 2024, a total of 70 cVDPV2 outbreaks from 34 emergences were reported in 38 countries (Figure 1) (Table); 532 AFP cases were confirmed in 26 countries. During the reporting period, five countries reported their first cVDPV2 detection since type 2-containing OPV was removed from OPV-using countries' routine immunization programs in April 2016. Ten (29%) of the 34 emergences spread outside the country of first detection. In Nigeria and Somalia, countries with security-compromised areas, persistent cVDPV2 transmission has spread frequently to neighboring countries. The transmission from Nigeria to its neighbors led to further international spread. The NIE-ZAS-1 emergence, first detected in Nigeria in July 2020, continued to circulate within Nigeria during the reporting period and was detected in 17 other countries in the African Region, particularly in West Africa (Figure 2). SOM-BAN-1, detected in Somalia in October 2017 (7), was reported in Kenya, and for the first time, was detected in Uganda during the reporting period. Since the previous reporting period (January 2021-December 2022) (7), Indonesia has detected two additional cVDPV2 emergences, with seven AFP cases. The EGY-NOR-1 emergence detected in 11 ES samples collected in Egypt was detected in six ES samples collected in the Palestinian Territories in June 2024 (Table).
Among the 70 cVDPV2 outbreaks, 29 (comprising 19 VDPV2 emergences) were linked to nOPV2 use in 19 countries. Two of the 19 emergences (RDC-SKV-1 and CAF-KEM-1) were first detected in September 2022 and December 2022, respectively. A total of 113 AFP cases were reported in 14 of the 19 countries with emergences; the highest number (70; 62%) was reported in DRC. Five countries detected outbreaks linked to nOPV2 use through ES only, with no confirmed AFP cases. The RDC-KOR-1 emergence was first detected in DRC in January 2023 and spread to Angola, Mozambique, and Republic of the Congo. The RDC-SKV-1 emergence was first detected in DRC and spread to Angola, Burundi, Côte d'Ivoire, Tanzania, and Zambia, with the most recent detection of an AFP case in Angola on May 11, 2024.
Of the 74 cVDPV outbreaks, 47 were new outbreaks detected during the reporting period in 30 of the 39 countries reporting outbreaks (Table). The remaining 27 outbreaks had been detected before the reporting period began and are ongoing (<13 months since most recent case) in 20 of the 39 countries. During January 2023-June 2024, SIAs were conducted to control cVDPV outbreaks in 32 of the 39 outbreak countries. Among the 74 cVDPV outbreaks, 11 (in seven countries) were documented to have been interrupted. Prolonged transmission of a cVDPV outbreak (≥12 months from first to most recent detection) was observed in 15 countries: Algeria, Benin, Cameroon, Central African Republic, Chad, Côte d'Ivoire, Democratic Republic of the Congo, Indonesia, Madagascar, Mali, Mozambique, Niger, Nigeria, Somalia, and Yemen. In seven of the 74 outbreaks across six countries, no cVDPV was detected ≥13 months since the most recent positive sample.