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Review 1: "Yellow Fever in Ghana: Predicting Emergence and Ecology from Historical Outbreaks"

While acknowledging the strengths of the studies, reviewers also offer constructive criticism regarding methodological clarity, data interpretation, and the need for updated references. 

Published onMar 08, 2024
Review 1: "Yellow Fever in Ghana: Predicting Emergence and Ecology from Historical Outbreaks"
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Yellow fever in Ghana: Predicting emergence and ecology from historical outbreaks
Yellow fever in Ghana: Predicting emergence and ecology from historical outbreaks
Description

Abstract Understanding the epidemiology and ecology of yellow fever in endemic regions is critical for preventing future outbreaks. Ghana is a high-risk country for yellow fever. In this study we estimate the epidemiology, ecological cycles, and areas at risk for yellow fever in Ghana based on historical outbreaks. We identify 2371 cases and 887 deaths (case fatality rate 37.4%) from yellow fever reported in Ghana from 1910 to 2022. Since implementation of routine childhood vaccination in 1992, the estimated mean annual number of cases decreased by 81% and the geographic distribution of yellow fever cases also changed. While there have been multiple large historical outbreaks of yellow fever in Ghana from the urban cycle, recent outbreaks have originated among unvaccinated nomadic groups in rural areas with the sylvatic/savanna cycles. Using machine learning and an ecological niche modeling framework, we predict areas in Ghana that are similar to where prior yellow fever outbreaks have originated based on temperature, precipitation, landcover, elevation, and human population density. We find differences in predictions depending on the ecological cycles of outbreaks. Ultimately, these findings and methods could be used to inform further subnational risk assessments for yellow fever in Ghana and other high-risk countries.Author Summary Yellow fever is a viral hemorrhagic fever transmitted by mosquitoes in Africa and South America through different ecological transmission cycles. While West Africa has had the most cases of yellow fever, less is known about the epidemiology and ecology of yellow fever among countries in this region. Ghana has had multiple yellow fever outbreaks, including a recent outbreak in 2021-2022. In this study we estimate cases and deaths due to yellow fever in Ghana, compare the ecological cycles of outbreaks, and predict future areas at risk based on prior yellow fever cases and environmental conditions. We find that the populations at risk for yellow fever in Ghana have changed over the past century and that different ecological factors influence the risk of future emergence. Understanding these changes and the nuances of yellow fever epidemiology and ecology within countries will be important for future outbreak preparedness.

RR:C19 Evidence Scale rating by reviewer:

  • Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.

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Review: Yellow fever (YF) is endemic in West Africa, the first definitive outbreak of YF in Ghana occurred in 1910, and since then Ghana has reported multiple outbreaks, with urban yellow fever occurring in six outbreaks. Here, the authors carried out a study on Yellow fever in Ghana: Predicting emergence and ecology from historical outbreaks. They estimated cases and deaths due to yellow fever in Ghana, compared the ecological cycles of outbreaks, and predicted future areas at risk based on prior yellow fever cases and environmental conditions. Using machine learning and an ecological niche modeling framework, they predicted areas in Ghana that are similar to where prior yellow fever outbreaks have originated based on temperature, precipitation, landcover, elevation, and human population density. After a critical appraisal, the following comments have been made:

  • Line 53-54: Too early, not preferred to start the introduction in this manner, provide a background first before telling readers about effective YF vaccines.

  • Line 56-62: Monath TP, Vasconcelos PFC. is a 2015 paper, provide new literature to site YF in sylvatic and savannah fronts in Africa.

  • Line 87-88: Recast without using numbers as references are in Vancouver style The core objectives of the EYE strategy are to (1) protect at-risk populations, (2) prevent international spread, and (3) contain outbreaks rapidly [8].

  • Line 103-104: Try to avoid numbering the objectives.

  • Line 108; Replace Setting with study location

  • Line 119-126 should not be there, kindly remove and place in the introduction.

  • Line 146: Stick to approved journal referencing style (Scott 1965) [21].

  • Line 236: Authors should explain the jackknife procedure that was used, and not assume that all the readers should know. 

  • Line 245: “we re-ran” to be changed to repeat

  • Line 368-369: Provide reference to support this important statement “Recent YF outbreaks appear to reflect the sylvatic and savanna cycles”.

  • Line 427: Given that there was sparse epidemiologic and entomologic surveillance data for most outbreaks why couldn’t the authors obtain data from elsewhere in Africa to buttress their submission.

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