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Letters

Study authors don’t consider waning SARS-CoV-2 immunity after vaccination in their model

James C. Doidge, Alex de Figueiredo, Trudo Lemmens and Kevin Bardosh
CMAJ June 20, 2022 194 (24) E847; DOI: https://doi.org/10.1503/cmaj.127321-l
James C. Doidge
Medical statistician, Intensive Care National Audit and Research Centre; London School of Hygiene and Tropical Medicine, London, UK
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Alex de Figueiredo
Statistician, Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK
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Trudo Lemmens
Professor and Scholl Chair in Health Law and Policy, Faculty of Law, University of Toronto, Toronto, Ont.
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Kevin Bardosh
Applied medical anthropologist, School of Public Health, University of Washington, Seattle, Wash.; Edinburgh Medical School, University of Edinburgh, Edinburgh, UK
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Fisman and colleagues1 present an oversimplification of a complex epidemiological, social and bioethical issue. The authors make strong ethical and political claims based on their findings, which feed existing social polarization.

The authors use a compartmental susceptible, infectious or recovered (SIR) model to compute the infection burden in vaccinated and unvaccinated population subgroups and assess the contribution of the unvaccinated group to the cumulative rate of infection among the vaccinated. The study’s main conclusion — that mixing with unvaccinated people increases the risk of infection among the vaccinated — is predetermined by the authors’ choice of model and parameters. By ignoring waning immunity (from both vaccination and previous infection), the authors have constructed a model in which herd immunity always occurs, leaving some residual proportion of the population uninfected indefinitely. In this hypothetical scenario, it is a foregone conclusion that if 1 group with high baseline immunity is mixed with another group of lower baseline immunity, then a greater proportion of the high-immunity group will become infected before herd immunity is achieved, compared with if they had not mixed. The model2 contains 2 crucial parameters: “vaccine efficacy” and “baseline immunity in unvaccinated.” If these are set to any combination where the latter is higher, then the findings are reversed; the vaccinated increase risk for the unvaccinated. Obviously, both conclusions are similarly flawed. In the context of observed waning of vaccine efficacy against infection,3 even the authors acknowledge that “it is unlikely that SARS-CoV-2 will be eliminated.” The authors discuss the theoretical risk that unvaccinated people pose to vaccinated people via their disproportionate demand for health care resources — something not considered in their model — without any acknowledgement of the vast difference in health care demands of, say, a healthy 18-year-old individual compared with an 80-year-old person with comorbidities. The potential for this work to foster social division and misplaced anger and blame is at odds with public health ethics.

Footnotes

  • Competing interests: None declared.

This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY-NC-ND 4.0) licence, which permits use, distribution and reproduction in any medium, provided that the original publication is properly cited, the use is noncommercial (i.e., research or educational use), and no modifications or adaptations are made. See: https://creativecommons.org/licenses/by-nc-nd/4.0/

References

  1. ↵
    1. Fisman DN,
    2. Amoako A,
    3. Tuite AR
    . Impact of population mixing between vaccinated and unvaccinated subpopulations on infectious disease dynamics: implications for SARS-CoV-2 transmission. CMAJ 2022;194:E573–80.
    OpenUrlAbstract/FREE Full Text
  2. ↵
    1. Fisman D,
    2. Tuite A
    . Simple 2-patch vaccine model. Figshare; 2022. Available: https://figshare.com/articles/dataset/Simple_2-Patch_Vaccine_Model/15189576 (accessed 2022 May 27).
  3. ↵
    1. Andrews N,
    2. Tessier E,
    3. Stowe J,
    4. et al
    . Duration of protection against mild and severe disease by COVID-19 vaccines. N Engl J Med 2022;386: 340–50.
    OpenUrlCrossRefPubMed
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Canadian Medical Association Journal: 194 (24)
CMAJ
Vol. 194, Issue 24
20 Jun 2022
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Study authors don’t consider waning SARS-CoV-2 immunity after vaccination in their model
James C. Doidge, Alex de Figueiredo, Trudo Lemmens, Kevin Bardosh
CMAJ Jun 2022, 194 (24) E847; DOI: 10.1503/cmaj.127321-l

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Study authors don’t consider waning SARS-CoV-2 immunity after vaccination in their model
James C. Doidge, Alex de Figueiredo, Trudo Lemmens, Kevin Bardosh
CMAJ Jun 2022, 194 (24) E847; DOI: 10.1503/cmaj.127321-l
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