This is an update on the yellow fever (YF) situation in the WHO African region published in the Event Information Site (EIS) announcement on 8 December 2021 and 26 August 2022 .
In 2022, 12 countries in the WHO African region have reported outbreaks of yellow fever (Cameroon, Central African Republic (CAR), Chad, Côte d’Ivoire, Democratic Republic of Congo (DRC), Ghana, Kenya, Niger, Nigeria, Republic of the Congo, Sierra Leone and Uganda). Eight of these countries are experiencing a continuation of transmission from 2021 (Cameroon, CAR, Chad, Côte d’Ivoire, DRC, Ghana, Nigeria, and Republic of the Congo) and four countries are newly reporting confirmed cases (Kenya, Niger, Sierra Leone and Uganda). One country, Gabon, reported cases in 2021, but no further cases were registered in 2022 indicating the end of the outbreak in Gabon.
From 1 January 2021 to 19 December 2022, a total of 203 confirmed and 252 probable cases with 40 deaths (CFR 9%) have been reported to WHO from 13 countries in the WHO African Region, with 49 additional plaque reduction neutralization test (PRNT) positive samples currently pending classification.
Since 5 August 2022 (data included in the previous EIS), a total of 22 additional confirmed cases have been reported from ten countries: Cameroon (1), CAR (3), Chad (6), Côte d’Ivoire (1), DRC (2), Ghana (1), Niger (4), Nigeria (2), Sierra Leone (1) and Uganda (1)). However, only seven confirmed cases had symptoms onset after 5 August 2022 and those were reported from four countries (CAR (2), Cameroon (1) Nigeria (2) and Niger (2) including one death from Niger. The rest of the cases were retrospectively classified as confirmed (with symptom onset prior to 5 August 2022), based on confirmatory tests performed and details obtained from investigations.
Since 2021, 40 deaths (CFR 9%) have been reported in the total 455 confirmed and probable cases. Of those, 23 deaths have been reported among confirmed cases (CFR 11%) (Table 1). The high global CFR among confirmed cases in 2021 (17 deaths, 11%) continued into 2022 (6 deaths, 12%) with multiple countries reporting CFRs above 1%.
The M:F ratio amongst confirmed cases was similar in 2021 and 2022 (1.3 and 1.6 respectively). The most affected age group amongst confirmed cases in 2021 was 10 years and below; meanwhile, the most affected group in 2022 is 20 to 30 years. Overall, about 71% of confirmed cases are aged 30 years and below and children aged 10 years and below seem particularly affected.
The majority of confirmed cases in the two year period were reported in the last quarter of 2021, with most from Ghana (62 cases, 12 deaths), Cameroon (35 cases, 0 deaths), Chad (30 cases, 5 deaths), Nigeria (24 cases, 0 deaths), and CAR (23 cases, 3 deaths). The other countries that have reported confirmed cases in the two year period are Côte d’Ivoire (8 cases, 0 deaths), DRC (6 cases, 1 death), Congo (4 cases, 0 deaths), Niger (4 cases, 1 death), Kenya (3 cases, 0 deaths), Uganda (2 cases, 0 deaths), Gabon (1 case, 0 death), and more recently Sierra Leone (1 case, 0 death). Countries including Burkina Faso, Senegal and Togo have reported probable cases that were subsequently discarded. One probable case from Benin is currently pending classification.
The M:F ratio amongst confirmed cases was similar in 2021 and 2022 (1.3 and 1.6 respectively). The most affected age group amongst confirmed cases in 2021 was 10 years and below; meanwhile, the most affected group in 2022 is 20 to 30 years. Overall, about 71% of confirmed cases are aged 30 years and below and children aged 10 years and below seem particularly affected. Approximately 48% of confirmed cases were in children and young adults <20 years which is greater than expected burden given that they were born after implementation of YF into routine immunization in many of the affected countries.
Several of the recent confirmations have been from urban areas and/or locations with little or no underlying immunity (e.g. near urban areas in Cameroon and Uganda; areas with no history of YF vaccination as in Isiolo, Kenya). Hard-to-reach and underserved populations have been disproportionately impacted.
Source: World Health Organization