Global yellow fever update, 2021/Mise a jour sur la fievre jaune dans le monde, 2021.

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Date: Aug. 12, 2022
From: Weekly Epidemiological Record(Vol. 97, Issue 32)
Publisher: World Health Organization
Document Type: Article
Length: 10,203 words
Lexile Measure: 1670L

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2021 in review

In 2021, yellow fever (YF) outbreaks were identified over a wide geographical area covering 11 countries in Africa, (1) while widespread virus circulation with occasional spill-over to humans continued in the Americas (Maps 1-3). The number of countries that reported confirmed and probable cases in the African Region was the highest in >20 years and was classified as a level-2 event in WHO's internal grading system for health emergencies on 30 November 2021. (2) In the Americas, YF cases were confirmed between June 2021 and June 2022 in settings with low population immunity in Bolivia (Plurinational State of), Brazil, French Guiana, Peru and Venezuela (Bolivarian Republic of).

YF transmission in Africa included outbreaks and cases in countries with a history of YF mass vaccination campaigns (Cameroon, Central African Republic, Ghana), escalating the concern raised by the re-emergence of outbreaks in West Africa in 2020. In 2021, those outbreaks affected populations that had not been reached by immunization services, including people living in areas with compromised security and people missed in large-scale campaigns. The resurgence of intense viral transmission highlights the importance of achieving and maintaining equitable, high vaccination coverage of all at-risk populations.

COVID-19 continued to impact YF control in 2021. The type of effect changed as countries prioritized vaccination against COVID-19, which led to postponement or de-prioritization of YF vaccination in some countries and affected vaccine acceptance. Despite the challenges, priority countries made good progress in implementing the Eliminate Yellow fever Epidemics (EYE) strategy in 2021, with >48 million people reached through reactive, catch-up and preventive YF vaccination campaigns in Africa.

Detailed epidemiological update

African Region

Because of the number of countries affected by confirmed acute YF cases and outbreaks from September 2021 (Map 1 and Table 1), the situation was graded by WHO to a level-2 health emergency on 30 November 2021 within the WHO Emergency Response Framework. The Region rapidly activated the incident management support team (IMST), and >14 technical assistance personnel were deployed by WHO to 7 countries, complemented by national personnel for investigation and response. The global stockpile of emergency YF vaccine managed through the International Coordination Group (ICG) was instrumental to enabling vaccination campaigns to interrupt outbreaks, with activities carrying into 2022.

The intensification of YF transmission might be due to a confluence of risk factors, including the natural cycle of virus transmission in jungle settings, growing gaps in immunity in areas that were previously protected, greater population movement (particularly informal), insecurity and gaps in routine immunization (RI) of underserved communities. Improvements in surveillance structures and testing of samples in national laboratories may also have increased the rate of detection. As shown in Table 3, Part B, further outbreaks may occur in other high-risk countries that completed campaigns previously but reported suboptimal RI coverage or in high-risk countries in which campaigns are currently planned in a context of suboptimal RI.

YF outbreaks and responses

* Ghana. Between 15 October 2021 and 31 December 2021, 61 probable and 60 confirmed YF cases were reported...

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Gale Document Number: GALE|A714778788