Sci Rep . Revisiting the link between COVID-19 incidence and infection fatality rate during the first pandemic wave

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Sci Rep


. 2025 May 5;15(1):15638.
doi: 10.1038/s41598-025-99078-6. Revisiting the link between COVID-19 incidence and infection fatality rate during the first pandemic wave

Benjamin Glemain ¹ , Charles Assaad ² , Walid Ghosn ³ , Paul Moulaire ² , Xavier de Lamballerie ⁴ , Marie Zins ^{5 6} , Gianluca Severi ^{7 8} , Mathilde Touvier ⁹ , Jean-François Deleuze ¹⁰ ; SAPRIS-SERO study group; Nathanaël Lapidus ¹¹ , Fabrice Carrat ^{# 11} , Pierre-Yves Ancel ^{# 12} , Marie-Aline Charles ¹² , Gianluca Severi ^{7 8} , Mathilde Touvier ⁹ , Marie Zins ^{5 6} , Sofiane Kab ⁶ , Adeline Renuy ⁶ , Stephane Le-Got ⁶ , Celine Ribet ⁶ , Mireille Pellicer ⁶ , Emmanuel Wiernik ⁶ , Marcel Goldberg ⁶ , Fanny Artaud ⁷ , Pascale Gerbouin-Rérolle ⁷ , Mélody Enguix ⁷ , Camille Laplanche ⁷ , Roselyn Gomes-Rima ⁷ , Lyan Hoang ⁷ , Emmanuelle Correia ⁷ , Alpha Amadou Barry ⁷ , Nadège Senina ⁷ , Julien Allegre ⁹ , Fabien Szabo de Edelenyi ⁹ , Nathalie Druesne-Pecollo ⁹ , Younes Esseddik ⁹ , Serge Hercberg ⁹ , Mélanie Deschasaux ⁹ , Marie-Aline Charles ¹² , Valérie Benhammou ¹³ , Anass Ritmi ¹⁴ , Laetitia Marchand ¹⁴ , Cecile Zaros ¹⁴ , Elodie Lordmi ¹⁴ , Adriana Candea ¹⁴ , Sophie de Visme ¹⁴ , Thierry Simeon ¹⁴ , Xavier Thierry ¹⁴ , Bertrand Geay ¹⁴ , Marie-Noelle Dufourg ¹⁴ , Karen Milcent ¹⁴ , Delphine Rahib ¹⁵ , Nathalie Lydie ¹⁵ , Clovis Lusivika-Nzinga ¹¹ , Gregory Pannetier ¹¹ , Nathanael Lapidus ¹¹ , Isabelle Goderel ¹¹ , Céline Dorival ¹¹ , Jérôme Nicol ¹¹ , Olivier Robineau ¹¹ , Cindy Lai ¹⁶ , Liza Belhadji ¹⁶ , Hélène Esperou ¹⁶ , Sandrine Couffin-Cadiergues ¹⁶ , Jean-Marie Gagliolo ¹⁷ , Hélène Blanché ¹⁰ , Jean-Marc Sébaoun ¹⁰ , Jean-Christophe Beaudoin ¹⁰ , Laetitia Gressin ¹⁰ , Valérie Morel ¹⁰ , Ouissam Ouili ¹⁰ , Jean-François Deleuze ¹⁰ , Laetitia Ninove ⁴ , Stéphane Priet ⁴ , Paola Mariela Saba Villarroel ⁴ , Toscane Fourié ⁴ , Souand Mohamed Ali ⁴ , Abdenour Amroun ⁴ , Morgan Seston ⁴ , Nazli Ayhan ⁴ , Boris Pastorino ⁴ , Xavier de Lamballerie ⁴



Affiliations

• PMID: 40325150
• PMCID: PMC12053613
• DOI: 10.1038/s41598-025-99078-6

Abstract

Several studies found an association between COVID-19 incidence, cumulated over the first pandemic wave, and the risk of death for infected individuals. They attributed this association to hospital overload. We studied this association across the French departments using 82,467 serological samples and a hierarchical Bayesian model with spatial smoothing. In high-incidence areas, we hypothesized that hospital overload would increase infection fatality rate (IFR) without increasing infection hospitalization rate (IHR). The analyses were adjusted for intensive care beds per capita, age of the population, and diabetes prevalence (as a surrogate for obesity). We found that increasing departmental incidence from 3 to 9% rose IFR from 0.42 to 1.14% (difference 0.72%, 95% CI 0.49-1.01%), and IHR from 1.66 to 3.61% (difference 1.94%, 95% CI 1.18-2.80%). An increase in incidence from 6 to 12% in people under 60 was associated with an increased proportion of people over 60 among those infected, from 11.6 to 17.4% (difference 5.8%, 95% CI 2.9-8.8%). Higher incidence increased the risk of death for infected individuals and their risk of hospitalization by the same magnitude. These findings could be explained by a higher age among infected individuals in high-incidence areas, rather by than hospital overload.

Keywords: Bayesian statistics; COVID-19; Causal graph; Hierarchical modeling; Hospital overload; Spatial modeling.