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Review 2: "Epidemiological Impact and Cost-Effectiveness Analysis of COVID-19 Vaccination in Kenya"

This study assesses the benefits of COVID-19 vaccines where most have already been exposed to SARS-CoV-2. Reviewers agree that their transmission modeling approach and sensitivity analyses were reliable, though further research in other counties would validate their findings.

Published onJan 03, 2023
Review 2: "Epidemiological Impact and Cost-Effectiveness Analysis of COVID-19 Vaccination in Kenya"
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key-enterThis Pub is a Review of
Epidemiological impact and cost-effectiveness analysis of COVID-19 vaccination in Kenya

ABSTRACTBackgroundFew studies have assessed the benefits of COVID-19 vaccines in settings where most of the population had been exposed to SARS-CoV-2 infection.MethodsWe conducted a cost-effectiveness analysis of COVID-19 vaccine in Kenya from a societal perspective over a 1.5-year time frame. An age-structured transmission model assumed at least 80% of the population to have prior natural immunity when an immune escape variant was introduced. We examine the effect of slow (18 months) or rapid (6 months) vaccine roll-out with vaccine coverage of 30%, 50% or 70% of the adult (> 18 years) population prioritizing roll-out in over 50-year olds (80% uptake in all scenarios). Cost data were obtained from primary analyses. We assumed vaccine procurement at $7 per dose and vaccine delivery costs of $3.90-$6.11 per dose. The cost-effectiveness threshold was USD 919.FindingsSlow roll-out at 30% coverage largely targets over 50-year-olds and resulted in 54% fewer deaths (8,132(7,914 to 8,373)) than no vaccination and was cost-saving (ICER=US$-1,343 (-1,345 to - 1,341) per DALY averted). Increasing coverage to 50% and 70%, further reduced deaths by 12% (810 (757 to 872) and 5% (282 (251 to 317) but was not cost-effective, using Kenya’s cost-effectiveness threshold ($ 919.11). Rapid roll-out with 30% coverage averted 63% more deaths and was more cost-saving (ICER=$-1,607 (-1,609 to -1,604) per DALY averted) compared to slow roll-out at the same coverage level, but 50% and 70% coverage scenarios were not cost-effective.InterpretationWith prior exposure partially protecting much of the Kenyan population, vaccination of young adults may no longer be cost-effective.KEY QUESTIONSWhat is already known?The COVID-19 pandemic has led to a substantial number of cases and deaths in low-and middle-income countries.COVID-19 vaccines are considered the main strategy of curtailing the pandemic. However, many African nations are still at the early phase of vaccination.Evidence on the cost-effectiveness of COVID-19 vaccines are useful in estimating value for money and illustrate opportunity costs. However, there is a need to balance these economic outcomes against the potential impact of vaccination.What are the new findings?In Kenya, a targeted vaccination strategy that prioritizes those of an older age and is deployed at a rapid rollout speed achieves greater marginal health impacts and is better value for money.Given the existing high-level population protection to COVID-19 due to prior exposure, vaccination of younger adults is less cost-effective in Kenya.What do the new findings imply?Rapid deployment of vaccines during a pandemic averts more cases, hospitalisations, and deaths and is more cost-effective.Against a context of constrained fiscal space for health, it is likely more prudent for Kenya to target those at severe risk of disease and possibly other vulnerable populations rather than to the whole population.

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.



This study updates an existing transmission model of SARS-CoV-2 in Kenya to include updated age- and vaccine status-related effects. The model is then used to predict cost-effectiveness of vaccination rollout campaigns, specifically focusing on treatment of young adults and the pace of rollout campaign. As with all decision-analytic modelling studies, parametric uncertainty may propagate into uncertainty in modelled results. The authors generally do a good job of quantifying and discussing this uncertainty.

The authors found that rapid rollout was dominant (reduces costs while improving health) compared to slower rollout. This result was similar to those from a previous South African study. The authors additionally found that, while vaccinating older adults was cost-effective, there were diminishing returns associated with vaccinating more young adults (in whom there was a high level of natural immunity). Further research in low- and middle-income countries to validate this finding would be informative, specifically focusing on whether optimal pricing mechanisms could improve the cost-effectiveness profile of the vaccine in currently cost-ineffective subgroups.

The authors conducted one-way and probabilistic sensitivity analysis to validate study findings. One minor concern is the small number of parameters employed in one-way sensitivity analysis. The only one-way sensitivity analyses conducted related to vaccine procurement costs and the discount rate of DALYs. One-way sensitivity analysis of all Table 2 “key parameters” would provide a broader sense of potential drivers of model uncertainty and help highlight areas for potential future research.

The authors employ the (relatively standard) approach of estimating societal costs of illness in proportion to GDP per capita. Gross domestic product has been shown to underestimate activity in the ‘informal’ labour market and other types of work (e.g., caretaking). Further sensitivity around the way productivity was monetized would be informative.


Since our solicitation of reviews, this preprint has been published in BMJ Global Health. The link to the published manuscript can be found here.

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