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Cited by 63SARS-CoV-2 and COVID-19 ResearchCOVID-19 Clinical Research StudiesCOVID-19 epidemiological studies

Severe hospital events following symptomatic infection with Sars-CoV-2 Omicron and Delta variants in France, December 2021–January 2022: A retrospective, population-based, matched cohort study

Open access
Auvigne, Vincent, Vaux, Sophie, Strat, Yann Le, Schaeffer, Justine, Fournier, Lucie, Tamandjou, Cynthia, Montagnat, Charline, Coignard, Bruno +2 more·2022·eClinicalMedicine
DOI 10.1016/j.eclinm.2022.101455PMC PMC9121907

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Abstract

Background: A rapid increase in incidence of the SARS-CoV-2 Omicron variant (sub-lineage BA.1) occurred in France in December 2021, while the Delta variant was prevailing since July 2021. We aimed to determine whether the risk of a severe hospital event following symptomatic SARS-CoV-2 infection differs for Omicron versus Delta. Methods: We conducted a retrospective cohort study to compare severe hospital events (admission to intensive care unit or death) between Omicron and Delta symptomatic cases matched according to week of virological diagnosis and age. The analysis was adjusted for age, sex, vaccination status, presence of comorbidities and region of residence, using Cox proportional hazards model. Findings: Between 06/12/2021-28/01/2022, 184 364 cases were included, of which 931 had a severe hospital event (822 Delta, 109 Omicron). The risk of severe event was lower among Omicron versus Delta cases; the difference in severity between the two variants decreased with age (adjusted Hazard Ratio (aHR)=0·13 95%CI: 0·08-0·20 among 40-64 years, aHR=0·50 95%CI: 0·26-0.98 among 80+ years). The risk of severe event increased with the presence of comorbidities (for very-high-risk comorbidity, aHR=4·15 95%CI: 2·86-6·01 among 40-64 years) and in males (aHR=2·28 95%CI: 1·82-2·85among 40-64 years) and was higher in unvaccinated compared to primo-vaccinated (aHR=7·29 95%CI: 5·58-9·54 among 40-64 years). A booster dose reduced the risk of severe hospital event in 80+ years infected with Omicron (aHR=0·29; 95%CI: 0·12-0·69). Interpretation: This study confirms the lower severity of Omicron compared to Delta. However, the difference in disease severity is less marked in the elderly. Further studies are needed to better understand the interactions between age and severity of variants. Funding: The study was performed as part of routine work at Public Health France.

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  • The conditional logistic regression models for vaccine effectiveness against symptomatic COVID-19 were adjusted for age, sex, type of residence, presence of at least one low or medium-risk comorbidity, and healthcare professional status.

    “The models included the variables age (as a continuous variable modelled using multiple fractional polynomials), sex, type of residence, presence of at least one low or medium-risk comorbidity (yes or no) [15], and healthcare professional status (yes or no) as covariates.”

    From Vaccine effectiveness and duration of protection of COVID-19 mRNA vaccines against Delta and Omicron BA.1 symptomatic and severe COVID-19 outcomes in adults aged 50 years and over in France (2023) · cites this paper as [15]

    The Statistical methods (p. 4) describe Cox proportional-hazards models for severe hospital events, not conditional logistic regression for vaccine effectiveness against symptomatic COVID-19. The Discussion (p. 8) explicitly says the study could not assess vaccines’ capacity to prevent symptomatic infection. Age, sex and comorbidities appear in its analyses, but that overlap does not support the attributed model or outcome. (LLM, conf=0.90)

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  • The Delta variant was characterized by higher transmissibility and severity compared to previously circulating SARS-CoV-2 strains.

    “The Delta variant was characterized by its higher transmissibility and severity compared to the previously circulating strains [15,16]”

    From Vaccine effectiveness and duration of protection of COVID-19 mRNA vaccines against Delta and Omicron BA.1 symptomatic and severe COVID-19 outcomes in adults aged 50 years and over in France (2023) · cites this paper as [15]

    The passage on p. 2 says Delta had higher transmissibility than the variants it replaced. The Summary (p. 1) finds Delta more severe than Omicron, but the paper does not establish that Delta was more severe than previously circulating strains. (LLM, conf=0.87)

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Research works printed but not linked: 24

  1. 1 Callaway E. Heavily mutated Omicron variant puts scientists on alert. Nature . 2021;600(7887):21. https://doi.org/10.1038/d41586021-03552-w. · DOI
  2. 2 WHO. Weekly epidemiological update on COVID-19 - 25 January 2022. Edition 76 . WHO; 2022. https://www.who.int/publications/m/ item/weekly-epidemiological-update-on-covid-19 -25-january2022. Accessed 26 January 2022. http://refhub.elsevier.com/S2589-5370(2200185-7/sbref0002)
  3. 5 Madhi SA, Kwatra G, Myers JE, Jassat W, Dhar N, Mukendi CK, et al. South African Population Immunity and Severe Covid-19 with Omicron Variant. medRxiv [preprint] . 2022. https://doi.org/ 10.1101/2021.12.20.21268096. · DOI
  4. 6 Abdullah F, Myers J, Basu D, et al. Decreased severity of disease during the first global omicron variant covid-19 outbreak in a large hospital in tshwane, south africa. Int J Infect Dis . 2021;116:38-42. https://doi.org/10.1016/j.ijid.2021.12.357. · DOI
  5. 7 Jassat WA, Karim AS, Mudara C, et al. Clinical severity of COVID19 patients admitted to hospitals in Gauteng, South Africa during the Omicrondominant fourth wave. SSRN [preprint] . 2021. https:// doi.org/10.2139/ssrn.3996320. [Internet][cited 2022 Jan 3]; Available from; https://ssrn.com/abstract=3996320. · DOI
  6. 8 Maslo C, Friedland R, Toubkin M, Laubscher A, Akaloo T, Kama B. Characteristics and outcomes of hospitalized patients in South Africa during the COVID-19 Omicron wave compared with previous waves. JAMA . 2021;327:583-584. https://doi.org/10.1001/jama.2021.24868. · DOI
  7. 9 Davies M-A, Kassanjee R, Rousseau P, Morden E, Johnson L, Solomon W, et al. Outcomes of laboratory-confirmed SARS-CoV-2 infection in the Omicron-driven fourth wave compared with previous waves in the Western Cape Province, South Africa. Tropical Medicine & International Health . 2022;Online ahead of print. https://doi.org/10.1111/tmi.13752. · DOI
  8. 11 Lefrancq N, Paireau J, Hoze N, et al. Evolution of outcomes for patients hospitalised during the first 9 months of the SARS-CoV-2 pandemic in France: a retrospective national surveillance data analysis. Lancet Reg Health Eur . 2021;5: 100087. https://doi.org/ 10.1016/j.lanepe.2021.100087. · DOI
  9. 12 Wolter N, Jassat W, Walaza S, Welch R, Moultrie H, Groome M, et al. Early assessment of the clinical severity of the SARS-CoV-2 Omicron variant in South Africa. medRXiv [preprint] . 2021. https:// doi.org/10.1101/2021.12.21.21268116. · DOI
  10. 13 Ulloa AC, Buchan SA, Daneman N, Brown KA. Early estimates of SARS-CoV-2 Omicron variant severity based on a matched cohort study, Ontario, Canada. medRxiv [preprint] . 2022. https://doi.org/ 10.1101/2021.12.24.21268382. · DOI
  11. 14 Lewnard JA, Hong VX, Patel MM, Kahn R, Lipsitch M, Tartof SY. Clinical outcomes among patients infected with Omicron (B.1.1.529) SARS-CoV-2 variant in southern California. medRxiv [preprint] . 2022. https://doi.org/10.1101/2022.01.11.22269045. · DOI
  12. 15 Nyberg T, Ferguson NM, Nash SG, et al. Comparative analysis of the risks of hospitalisation and death associated with SARS-CoV-2 omicron (B.1.1.529) and delta (B.1.617.2) variants in England: a cohort study. Lancet . 2022;399(10332):1303-1312. https://doi.org/ 10.1016/S0140-6736(22)00462-7. · DOI · Paper page
  13. 16 Veneti L, Bøa s H, Bra then Kristoffersen A, et al. Reduced risk of hospitalisation among reported COVID-19 cases infected with the SARS-CoV-2 Omicron BA.1 variant compared with the Delta variant, Norway, December 2021 to January 2022. Eurosurveillance . 2022;27:(4) 2200077. https://doi.org/10.2807/1560-7917. ES.2022.27.4.2200077. · DOI
  14. 17 Lu L, Mok BW, Chen LL, et al. Neutralization of SARS-CoV-2 Omicron variant by sera from BNT162b2 or Coronavac vaccine recipients. Clin Infect Dis . 2021. https://doi.org/10.1093/cid/ciab1041. · DOI
  15. 18 Collie S, Champion J, Moultrie H, Bekker LG, Gray G. Effectiveness of BNT162b2 Vaccine against Omicron Variant in South Africa. N Engl J Med . 2021;386:494-496. https://doi.org/10.1056/ NEJMc2119270.
  16. 19 GeurtsvanKessel CH, Geers D, Schmitz KS, et al. Divergent SARS CoV-2 Omicron-reactive T- and B cell responses in COVID-19 vaccine recipients. Sci Immunol . 2022;7(69):eabo2202. https://doi. org/10.1126/sciimmunol.abo2202. · DOI
  17. 20 Liu J, Chandrashekar A, Sellers D, Barrett J, Jacob-Dolan C, Lifton M, et al. Vaccines elicit highly conserved cellular immunity to SARS-CoV-2 Omicron. Nature . 2022;603:493-496. https://doi. org/10.1038/s41586-022-04465-y. · DOI
  18. 21 Keeton R, Tincho MB, Ngomti A, et al. T cell responses to SARSCoV-2 spike cross-recognize Omicron. Nature . 2022;603:488-492. https://doi.org/10.1038/s41586-022-04460-3. · DOI
  19. 22 Bentley EG, Kirby A, Sharma P, Kipar A, Mega DF, Bramwell C, et al. SARS-CoV-2 Omicron-B.1.1.529 Variant leads to less severe disease than Pango B and Delta variants strains in a mouse model of severe COVID-19. BioRxiv [preprint] . 2021. https://doi.org/ 10.1101/2021.12.26.474085. · DOI
  20. 23 Halfmann PJ, Iida S, Iwatsuki-Horimoto K, Maemura T, Kiso M, Scheaffer SM, et al. SARS-CoV-2 Omicron virus causes attenuated disease in mice and hamsters. Nature . 2022;603:687-692. https:// doi.org/10.1038/s41586-022-04441-6. · DOI
  21. 24 Hui KPY, Ho JCW, Cheung MC, et al. SARS-CoV-2 Omicron variant replication in human bronchus and lung ex vivo . Nature . 2022;603:715-720. https://doi.org/10.1038/s41586-022-04479-6. · DOI
  22. 27 Gebhard C, Regitz-Zagrosek V, Neuhauser HK, Morgan R, Klein SL. Impact of sex and gender on COVID-19 outcomes in Europe. Biol Sex Differ . 2020;11(1):29. https://doi.org/10.1186/s13293-02000304-9. · DOI
  23. 28 Jin JM, Bai P, He W, et al. Gender differences in patients with COVID-19: focus on severity and mortality. Front Public Health . 2020;8:152. https://doi.org/10.3389/fpubh.2020.00152. · DOI
  24. 29 Bastard J, Taisne B, Figoni J, et al. Impact of the Omicron variant on SARS-CoV-2 reinfections in France, March 2021 to February 2022. Eurosurveillance . 2022;27:(13) 2200247. https://doi.org/ 10.2807/1560-7917.ES.2022.27.13.2200247. · DOI

Cited by

Sorted by citations

Authors
Auvigne, V., Vaux, S., Strat, Y. L., Schaeffer, J., Fournier, L., Tamandjou, C., Montagnat, C., Coignard, B., Levy-Bruhl, D., & Parent du Châtelet, I.
Affiliations
Santé Publique France (FR)
Corresponding author
Auvigne, Vincent
ORCID
Venue
eClinicalMedicine
Publisher
Elsevier BV
Published
2022-06
Volume
48
Pages
101455
ISSN
2589-5370 (ISSN-L)
DOI
10.1016/j.eclinm.2022.101455
PMC
PMC9121907
OpenAlex
W4280630418
Cited by
63
References
3
Citations by year
2026: 1 · 2025: 5 · 2024: 10 · 2023: 31 · 2022: 16
FWCI
7.58
Type
journal article
Language
en
Open access
Licence
Locations
  • EClinicalMedicine (publishedVersion, cc-by-nc-nd)
  • medRxiv (acceptedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by-nc-nd)
  • PubMed (publishedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Topics
  • Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
  • Health Sciences › Medicine › Infectious Diseases › COVID-19 Clinical Research Studies
  • Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
Keywords
Delta variant, symptomatic COVID-19, intensive care unit admission, COVID-19 mortality, comorbidities, vaccination status, booster vaccination, matched cohort

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