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Review 1: "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 1: "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 modelling study examines the impact and cost-effective that alternative COVID-19 vaccine rollout strategies may have had. Vaccination is assumed to be rolled out from the peak of the Delta wave in September 2021 and to take either 18 months (non-rapid deployment) or 6 months (rapid deployment). Such a programme is too late to avoid most of the burden associated with the Delta wave, but could help to mitigate a later wave due to an immune escape (Omicron-like) variant that emerges in late 2021. The analysis found this variant would cause a large wave of hospitalisations and deaths in late 2021/early 2022. This did actually happen even though the severity of this wave was mitigated by the relatively low severity of Kenya and the start of the vaccine rollout. The modelling indicates that rapid vaccine development focused on the most vulnerable adults (those aged over 50 years old) has the potential to prevent many of the deaths associated with the new wave and be cost-effective. Extending such a programme to include many younger adults would have only a small incremental effect on deaths and not be cost-effective.

Modelling transmission of SARS-CoV-2 and its associated health burden has been challenging across the world, due to under-reporting of cases, hospitalisations and deaths, as well as the changing effect of variant emergence and vaccine rollout. This study uses an appropriate approach to deal with the challenges, including incorporating data from PCR testing and serology in a Bayesian framework that also leverages information on reporting from other countries. Sensitivity analyses indicate that the broad conclusions are fairly robust, unless there is virtually no under-reporting of hospitalizations and deaths in which case vaccination stops being cost-effective.

The most important conclusion is that vaccination of younger adults has relatively little impact and is not cost-effective, partly because of immunity from prior exposure in this population and the limited impact of vaccination to reduce transmission. This conclusion is plausible given the data and modelling, but some caution should be taken before it is extrapolated as a general conclusion to other settings, times or variants as it may be dependent on the exact level of population immunity to the variant from natural infection vs. vaccination.


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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