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. 2023 Aug 14;77(3):355-361.
doi: 10.1093/cid/ciad210.

Changes in Population Immunity Against Infection and Severe Disease From Severe Acute Respiratory Syndrome Coronavirus 2 Omicron Variants in the United States Between December 2021 and November 2022

Fayette Klaassen  1 , Melanie H Chitwood  2 , Ted Cohen  2 , Virginia E Pitzer  2 , Marcus Russi  2 , Nicole A Swartwood  1 , Joshua A Salomon  3 , Nicolas A Menzies  1
Affiliations

Changes in Population Immunity Against Infection and Severe Disease From Severe Acute Respiratory Syndrome Coronavirus 2 Omicron Variants in the United States Between December 2021 and November 2022

Fayette Klaassen et al. Clin Infect Dis. .

Abstract

Background: Although a substantial fraction of the US population was infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during December 2021-February 2022, the subsequent evolution of population immunity reflects the competing influences of waning protection over time and acquisition or restoration of immunity through additional infections and vaccinations.

Methods: Using a Bayesian evidence synthesis model of reported coronavirus disease 2019 (COVID-19) data (diagnoses, hospitalizations), vaccinations, and waning patterns for vaccine- and infection-acquired immunity, we estimate population immunity against infection and severe disease from SARS-CoV-2 Omicron variants in the United States, by location (national, state, county) and week.

Results: By 9 November 2022, 97% (95%-99%) of the US population were estimated to have prior immunological exposure to SARS-CoV-2. Between 1 December 2021 and 9 November 2022, protection against a new Omicron infection rose from 22% (21%-23%) to 63% (51%-75%) nationally, and protection against an Omicron infection leading to severe disease increased from 61% (59%-64%) to 89% (83%-92%). Increasing first booster uptake to 55% in all states (current US coverage: 34%) and second booster uptake to 22% (current US coverage: 11%) would increase protection against infection by 4.5 percentage points (2.4-7.2) and protection against severe disease by 1.1 percentage points (1.0-1.5).

Conclusions: Effective protection against SARS-CoV-2 infection and severe disease in November 2022 was substantially higher than in December 2021. Despite this high level of protection, a more transmissible or immune evading (sub)variant, changes in behavior, or ongoing waning of immunity could lead to a new SARS-CoV-2 wave.

Keywords: Omicron variants; SARS-CoV-2; effective protection; immunological exposure.

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Conflict of interest statement

Potential conflicts of interest. V. E. P. reports grants from Bill & Melinda Gates Foundation, US CDC, Gavi, the Vaccine Alliance, NIH/NIAID, Wellcome Trust, and NIHR (UK) (grant to institution), and is a member for World Health Organization (WHO) IVIR-AC. N. A. M. reports grants from WHO, Bill & Melinda Gates Foundation, US CDC, and NIH, and consulting fees from The Global Fund to Fight AIDS, Tuberculosis, and Malaria (paid to author). N. A. S. reports grants or contracts from CDC and NIH. M. H. C. reports support for attending meetings and/or travel from WHO Global Task Force on TB Impact Measurement. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

Figures

Graphical Abstract
Graphical Abstract
This graphical abstract is also available at Tidbit: https://tidbitapp.io/tidbits/changes-in-population-immunity-against-infection-and-severe-disease-from-sars-cov-2-omicron-variants-in-the-united-states-between-december-2021-and-november-2022-f6e0374e-e984-44b9-814b-2347a8bc7503
Figure 1.
Figure 1.
Assumed initial immunity and waning trends for different combinations of prior infection and vaccination.
Figure 2.
Figure 2.
Flow of the US population between COVID-19 starting exposure states on 1 December 2021 to ending exposure state on 9 November 2022. F Individuals may make multiple transitions over this time period. Abbreviation: COVID-19, coronavirus disease 2019.
Figure 3.
Figure 3.
Population protection against infection (A and B) and severe disease (C and D) from the Omicron variant in the United States population between 1 December 2021 and 9 November 2022, by exposure state (A and C) and waning scenario (B and D).
Figure 4.
Figure 4.
State-level changes in population protection against infection and severe disease from the Omicron variant between 1 December 2021 and 9 November 2022.
See this image and copyright information in PMC

Update of

References

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