Cited by 1,009SARS-CoV-2 and COVID-19 ResearchCOVID-19 Clinical Research StudiesCOVID-19 epidemiological studies

The DOI matches its Crossref record; 281 of the 281 references it cites were found in a registry or an index; 24 of the 147 sources its claims cite were checked for support.

The biological and clinical significance of emerging SARS-CoV-2 variants

Open access
Tao, Kaiming, Tzou, Philip L., Nouhin, Janin, Gupta, Ravindra K., de Oliveira, Tulio, Kosakovsky Pond, Sergei L., Fera, Daniela, Shafer, Robert W.·2021·Nature Reviews Genetics

Abstract

The past several months have witnessed the emergence of SARS-CoV-2 variants with novel spike protein mutations that are influencing the epidemiological and clinical aspects of the COVID-19 pandemic. These variants can increase rates of virus transmission and/or increase the risk of reinfection and reduce the protection afforded by neutralizing monoclonal antibodies and vaccination. These variants can therefore enable SARS-CoV-2 to continue its spread in the face of rising population immunity while maintaining or increasing its replication fitness. The identification of four rapidly expanding virus lineages since December 2020, designated variants of concern, has ushered in a new stage of the pandemic. The four variants of concern, the Alpha variant (originally identified in the UK), the Beta variant (originally identified in South Africa), the Gamma variant (originally identified in Brazil) and the Delta variant (originally identified in India), share several mutations with one another as well as with an increasing number of other recently identified SARS-CoV-2 variants. Collectively, these SARS-CoV-2 variants complicate the COVID-19 research agenda and necessitate additional avenues of laboratory, epidemiological and clinical research. In this Review, the authors describe our latest understanding of the emergence and properties of SARS-CoV-2 genetic variants, particularly those designated as WHO (World Health Organization) ‘variants of concern’. They focus on the consequences of these variants for antibody-mediated virus neutralization, with important implications for reinfection risk and for vaccine effectiveness.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

This review synthesizes SARS-CoV-2 evolution, spike structure and the biological/clinical significance of the four WHO variants of concern as of June 2021: Alpha, Beta, Gamma and Delta. It shows that recurrent spike mutations increase transmissibility and immune evasion, reducing neutralization by monoclonal antibodies and vaccinee plasma, and calls for integrated genomic, neutralization and vaccine-efficacy surveillance.

Key findings

  • Four VOCs emerged independently: Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1) and Delta (B.1.617.2). Alpha was estimated to be ~50% more transmissible than prior UK variants and associated with an estimated 50% increased mortality; Beta was estimated to be 50% more transmissible than preceding lineages; Gamma was estimated to cause 3–4 times higher virus levels and 1.1-fold to 1.8-fold higher mortality; Delta spread to 54 countries and replaced Alpha in the UK and USA.
  • Neutralization escape varied by variant. Beta showed 3-fold to 10-fold reduced susceptibility to 46% and >10-fold reduced susceptibility to 22% of convalescent plasma samples; mRNA vaccinee plasma showed 45% with 3-fold to 10-fold and 30% with >10-fold reduced Beta neutralization. Delta showed 3-fold to 10-fold reduced susceptibility to 45% and >10-fold to 5% of convalescent plasma samples, while ~15% of BNT162b vaccinee plasma had 3-fold to 10-fold reduced Delta neutralization. Alpha was rarely associated with reduced convalescent plasma susceptibility but showed 3-fold to 10-fold reduced susceptibility to ~15% of mRNA vaccinee plasma samples.
  • Vaccine efficacy against VOCs was reduced in several studies: BNT162b retained >90% efficacy against Alpha in Israel and Qatar; Beta efficacy was 72% in a Qatar cohort and 75% in a test-negative case-control study; Delta efficacy was ~85% for BNT162b and ~60% for AZD1222 in UK case-control studies. In trials, AZD1222 efficacy against Beta was 10% in South Africa, and NVX-CoV2373 efficacy was 49% against Beta and 86.3% against Alpha versus 96.4% against non-Alpha variants.
  • Key mutations include D614G, which rose to near 100% global prevalence by June 2020; N501Y, which increases ACE2 affinity; E484K, which reduces susceptibility to several monoclonal antibodies and plasma; and non-spike mutations that antagonize innate immunity, with Alpha and Beta showing mean 112-fold and 8-fold reduced susceptibility to type I interferons, respectively, compared with an early pandemic virus.

Methods

  • Narrative review creating a framework for SARS-CoV-2 variants by describing evolution, spike protein structure/function, laboratory characterization methods, biological and epidemiological properties of VOCs/VOIs, and required research responses; data summarized as of June 2021.
  • Synthesizes genomic surveillance data from more than two million partially or fully sequenced virus isolates, in vitro selection and neutralization experiments using pseudotyped viruses, VSV-based chimeric viruses, full-length recombinant SARS-CoV-2 and cultured isolates, deep mutational scanning, and vaccine efficacy trials, test-negative case-control studies and cohort studies.
  • Neutralization results were pooled in the Stanford University Coronavirus Antiviral & Resistance Database and summarized as <3-fold, 3–10-fold and >10-fold reductions compared with control viruses.

Limitations

  • The paper states that as of June 2021 it is uncertain whether current lineage-based variant classification will be sustainable, and that classifying variants by component mutations may become challenging if recurrent mutations increase.
  • The paper notes unresolved questions, including whether neutralizing antibodies are the most important protective mechanism versus memory B cells, Fc-effector functions and T cell immunity, and whether updated immunogens can broaden responses in animal models more predictive of humans.
  • Evident from the text: this is a synthesis as of June 2021, so later variants and data are not included; neutralization estimates pool results across pseudotyped, chimeric and infectious virus assays, and some distributions are approximate because they include results reported only as aggregate mean fold reductions.

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Integrity signals

Registry

Crossref · 10.1038/s41576-021-00408-x

Cites

281 of 281 references verified0 citation errors · 0 not checkable

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  1. Edara, V. V., Hudson, W. H., Xie, X., Ahmed, R. & Suthar, M. S. Neutralizing antibodies against SARS-CoV-2 variants after infection and vaccination. JAMA 325, 1896–1898 (2021). · DOI · Paper page

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Metadata

Authors
Tao, K., Tzou, P. L., Nouhin, J., Gupta, R. K., de Oliveira, T., Kosakovsky Pond, S. L., Fera, D., & Shafer, R. W.
Affiliations
  • Stanford Medicine (US)
  • University of Cambridge (GB)
  • Swarthmore College (US)
Corresponding author
Shafer, Robert W.
Venue
Nature Reviews Genetics
Published
2021-09-17
Volume
22
Issue
12
Pages
757-773
ISSN
  • 1471-0056 (ISSN-L)
  • 1471-0064
OpenAlex
W3199849883
Cited by
1,009
References
281
Citations by year
2026: 43 · 2025: 90 · 2024: 170 · 2023: 251 · 2022: 415 · 2021: 38
FWCI
25.63
Type
journal article
Language
en
Open access
Locations
  • Nature Reviews Genetics (publishedVersion, cc-by)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • Works - Scholarship, Research, & Creative Expression (Swarthmore College) (submittedVersion)
Funders
  • University of Washington
  • National Institute of Allergy and Infectious Diseases (R24AI136618)
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
SARS-CoV-2, COVID-19 variants of concern, spike protein mutations, Alpha variant, Beta variant, Gamma variant, Delta variant, virus transmission, reinfection risk, neutralizing antibodies, vaccine effectiveness, herd immunity, viral replication fitness
MeSH terms
COVID-19, SARS-CoV-2, Epitopes, Biological Evolution, Humans, Mutation, Spike Glycoprotein, Coronavirus

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