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Review 1: "The Impact of Vaccination on COVID-19 Outbreaks in the United States"

Published onMar 31, 2022
Review 1: "The Impact of Vaccination on COVID-19 Outbreaks in the United States"
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key-enterThis Pub is a Review of
The impact of vaccination on COVID-19 outbreaks in the United States

AbstractBackgroundGlobal vaccine development efforts have been accelerated in response to the devastating COVID-19 pandemic. We evaluated the impact of a 2-dose COVID-19 vaccination campaign on reducing incidence, hospitalizations, and deaths in the United States (US).MethodsWe developed an agent-based model of SARS-CoV-2 transmission and parameterized it with US demographics and age-specific COVID-19 outcomes. Healthcare workers and high-risk individuals were prioritized for vaccination, while children under 18 years of age were not vaccinated. We considered a vaccine efficacy of 95% against disease following 2 doses administered 21 days apart achieving 40% vaccine coverage of the overall population within 284 days. We varied vaccine efficacy against infection, and specified 10% pre-existing population immunity for the base-case scenario. The model was calibrated to an effective reproduction number of 1.2, accounting for current non-pharmaceutical interventions in the US.ResultsVaccination reduced the overall attack rate to 4.6% (95% CrI: 4.3% - 5.0%) from 9.0% (95% CrI: 8.4% - 9.4%) without vaccination, over 300 days. The highest relative reduction (54-62%) was observed among individuals aged 65 and older. Vaccination markedly reduced adverse outcomes, with non-ICU hospitalizations, ICU hospitalizations, and deaths decreasing by 63.5% (95% CrI: 60.3% - 66.7%), 65.6% (95% CrI: 62.2% - 68.6%), and 69.3% (95% CrI: 65.5% - 73.1%), respectively, across the same period.ConclusionsOur results indicate that vaccination can have a substantial impact on mitigating COVID-19 outbreaks, even with limited protection against infection. However, continued compliance with non-pharmaceutical interventions is essential to achieve this impact.Key pointsVaccination with a 95% efficacy against disease could substantially mitigate future attack rates, hospitalizations, and deaths, even if only adults are vaccinated. Non-pharmaceutical interventions remain an important part of outbreak response as vaccines are distributed over time.

RR:C19 Evidence Scale rating by reviewer:

  • Strong. The main study claims are very well-justified by the data and analytic methods used. There is little room for doubt that the study produced has very similar results and conclusions as compared with the hypothetical ideal study. The study’s main claims should be considered conclusive and actionable without reservation.



The study concludes from simulation based on an agent-based model that vaccination could have a substantial impact in reduction of adverse outcomes with non-ICU, ICU hospitalization and deaths among individuals 65 and older in the United States. The agent-based model used for the simulation is based on a standard epidemiological modelling and is appropriate for evaluating the effect of a vaccine on COVID-19 in the United States. The main conclusion is convincing and such result is also timely since the approved vaccines would be administered to individuals covered in this study. A general remark concerning the model/research is that models/research of this type have been formulated to study the impact of vaccination on COVID-19 in the United States (Enahoro Iboi, Calistus Ngonghala, and Abba Gumel. Gumel. Will an imperfect vaccine curtail the COVID-19 pandemic in the US? Infectious Disease Modeling. 5 (2020) 510-524). This connection should be clearly stated in other to compare results here to those found in Iboi et al. Adding the corresponding references would cover relevant literature adequately.

The major conclusion is of crucial importance to the general public and public health experts regarding the outcome of prioritizing the COVID vaccine on healthcare workers and people with pre-existing conditions.


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