Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2022 May;22(5):267-269.
doi: 10.1038/s41577-022-00720-5.

Estimating disease severity of Omicron and Delta SARS-CoV-2 infections

Alex Sigal  1   2   3   4 , Ron Milo  5 , Waasila Jassat  6   7
Affiliations

Estimating disease severity of Omicron and Delta SARS-CoV-2 infections

Alex Sigal et al. Nat Rev Immunol. 2022 May.

Abstract

The Omicron variant of SARS-CoV-2 has been reported to cause milder disease in adults but lead to increased hospital admissions in children. How can we compare disease severity in Omicron and Delta infections, and how should differences be interpreted?

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Estimating disease severity.
a | A simplified severity scale for COVID-19 disease. b | Ballpark estimate of the fraction of unreported infections based on UK surveillance data. c | Periods for the USA Delta (15 July 2021 to 15 November 2021) and Omicron (15 December 2021 to 15 March 2022) infection waves used in the analysis. The period between 15 November and 15 December was not analysed to avoid times when both variants were circulating. d,e | Cumulative number of deaths (d) and reported cases (e) since the start of each infection wave from Centers for Disease Control and Prevention (CDC) data. f | Cumulative number of estimated total infections in each wave, calculated by dividing the number of cumulative reported cases by the UK estimated fraction of reported to total infections as determined from data in (b). g | Case fatality ratio, the cumulative number of deaths divided by the cumulative number of reported infections per wave. h | Infection fatality ratio, the cumulative number of deaths divided by the cumulative number of estimated total infections per wave.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Abdullah F, 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. doi: 10.1016/j.ijid.2021.12.357. - DOI - PMC - PubMed
    1. Sigal A. Milder disease with Omicron: is it the virus or the pre-existing immunity? Nat. Rev. Immunol. 2022;22:69–71. doi: 10.1038/s41577-022-00678-4. - DOI - PMC - PubMed
    1. New York State Department of Health. Pediatric COVID-19 update: January 7, 2022 https://www.health.ny.gov/press/releases/2022/docs/pediatric_covid-19_ho... (2022).
    1. UK Health Security Agency. SARS-CoV-2 variants of concern and variants under investigation in England. Technical briefing 34 https://assets.publishing.service.gov.uk/government/uploads/system/uploa... (2022).
    1. Garret N, et al. High rate of asymptomatic carriage associated with variant strain Omicron. medRxiv. 2021 doi: 10.1101/2021.12.20.21268130. - DOI