WHO alerts Nigeria, 8 others of resurgence in yellow fever cases
World Health Organisation (WHO) has alerted Nigeria, as well as eight other countries in Africa iof a possible resurgence of the yellow fever disease in their territories, adding that it has confirmed 300 probable and 88 laboratory cases of the illness, since the beginning of 2021 and as of 20 December 20, this year.
The WHO African Region listed the other countries as Cameroon, Chad, Central African Republic (CAR), Côte d’Ivoire, Democratic Republic of Congo (DRC), Ghana, Niger, and Republic of Congo, as having reported human laboratory confirmation yellow fever (YF) cases, even as it labeled them as being at ‘high risk for the disease and have a history of transmission and outbreaks of the disease.’
“These outbreaks are growing in case numbers, necessitating an urgent response.
“Among the probable cases there have been 66 deaths reported from six countries (Ghana – 42; Cameroon – 8; Chad – 8; Nigeria – 4; Congo – 2; DRC – 2), the overall case fatality ratio (CFR) among the probable cases is 22%, with a very wide variation among countries; Ghana (40%) and Cameroon (21%).
“In October and November 2021, confirmed active YF outbreaks were reported in Ghana and Chad respectively and required support from the International Coordinating Group (ICG) for vaccine provision from the emergency global stockpile of YF vaccine.
“Among the affected countries some are classified as having a fragile, conflict-affected or vulnerable (FCV) setting, in addition to low YF population immunity. Gaps or delays in investigations of suspected YF cases due to insecurity (Chad, Cameroon, CAR) or under-served (nomadic) communities (Ghana) have implications for harm to human health and risk of onward amplification and spread,” said WHO.
The global health body said the situation is also concerning where cases have been confirmed in inaccessible health districts with weak YF surveillance, preparedness, and response systems, and significant population displacements into neighbouring countries (like Cameroon, Chad, CAR).
“In addition, there are major urban areas such as Abidjan, Cote d’Ivoire that have reported YF cases and are a high concern as they pose a significant risk of amplification mediated by Aedes aegypti person-mosquito-person transmission (without sylvatic intermediary).
“Urban YF outbreaks can rapidly amplify with onward spread internationally, as seen in Angola and DRC in 2016. The case count of confirmed and probable cases is rapidly evolving and has challenges to track due to the complexity of interpretation in the context of available epidemiological and clinical data, including vaccination history of the cases.
“The overall YF vaccination coverage in these regions is not sufficient to provide herd immunity and prevent outbreaks. Estimates from WHO and UNICEF in 2020 on routine YF vaccination coverage was 44% in the African region, much lower than the 80% threshold required to confer herd immunity against YF.
“The national coverage in the countries of concern were all under 80% with the exception of Ghana (88%): Congo (69%), Cote D’Ivoire (69%), Niger (67%), Cameroon (57%), DRC (56%), Nigeria (54%), CAR (41%), and Chad (35%). These low YF vaccination coverages indicate the presence of an underlying susceptible population at risk of YF and a risk of continued transmission,” WHO said.
Continuing, WHO pointed out that these outbreaks are occurring in a large geographic area in the West and Central regions of Africa.
“These reports signal a resurgence and intensified transmission of the YF virus. The outbreaks have included areas that have previously conducted large-scale mass vaccination campaigns but with persistent and growing gaps in immunity due to lack of sustained population immunity through routine immunization and/or secondary to population movements (newcomers without history of vaccination). “For example, outbreaks were identified in late 2020 in countries with a history of nationwide preventive mass vaccination campaigns (PMVCs) including an outbreak in Guinea notified in November 2020 (history of PMVCs 2005, 2010) and Senegal notified in November 2020, (history of PMVCs 2007 plus reactive campaigns in 2011, 2005, 2002). In 2021, the recently confirmed outbreak in Ghana is marked by an impact on nomadic communities, despite the country having completed the final phase of PMVC in November 2020. Outbreaks and case reports of suspected, probable and/or confirmed cases are also occurring in other settings in the region where nationwide phased PMVCs are ongoing and yet to be completed (DRC, Nigeria), or yet to be initiated (Chad, Niger), further compounding the risk of spread.
“Another potential factor contributing to the enhanced risk is a delay in the investigation of probable cases. The investigation of probable cases has faced challenges in many of the reporting countries made complicated due to stretched resources, capacity, and logistical challenges. The health systems in the nine countries with confirmed YF, in addition to the COVID-19 pandemic and COVID-19 vaccine rollout, have been strained with many other competing acute public health outbreaks which has diverted attention from YF preparedness and response activities.
“The numerous YF cases and outbreaks in a broad geographic scope, with upward trend of confirmed cases and outbreaks, is indication of ongoing intense YF virus transmission in an extended area in the region and represent a persistent and growing risk to all unvaccinated people living or visiting YF high-risk countries,” said WHO.
