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Living Evidence - SARS-CoV-2 variants

Living evidence tables provide high level summaries of key studies and evidence on a particular topic, and links to sources. They are reviewed regularly and updated as new evidence and information is published.

Viruses constantly change through mutation and over time, new variants of a virus are expected to occur. Some variants have characteristics that have a significant impact on transmissibility, severity of disease and effectiveness of vaccines.  This table includes information on variants that are currently causing concern in the scientific community.

Currently, the World Health Organization  has identified four variants of concern: Alpha, Beta, Gamma and Delta.

Daily checks are conducted for new content and any updates that occur during the week are highlighted. All highlights are removed each Monday.

  Alpha (B.1.1.7) Beta (B.1.351) Gamma (P.1) Delta (B.1.617.2)
WHO label Alpha Beta Gamma Delta
Scientific names

B.1.1.7

GRY (formerly GR/501Y.V1)

20I/S:501Y.V1

Variant of Concern (VOC) - 202012/01

B.1.351

GH/501Y.V2

20H/S:501Y.V2

Variant of Concern (VOC) – 202012/02

B.1.1.28.1 (P.1)

GR/501Y.V3

20J/S:501Y.V3

Variant of Concern (VOC) – 202101/02

B.1.617.2

G/452.V3

21A/S:478K

Variant of Concern (VOC) - VOC-21APR-02

First detected

UK

September 2020

South Africa

May 2020

Brazil

November 2020

India

October 2020

Mutations 23 (17 of which change amino acids)

Includes N501Y substitution

21 (8 of which change amino acids)

Includes N501Y substitution

17 (11 of which change amino acids)

Includes N501Y substitution

12

Includes spike mutation profiles L452R, E484Q and D614G and lacks mutations at amino acid positions 501 or 484 in its ACE2 receptor.

P681R change is a crucial feature of Delta*^

Characterised by an excess of non-synonymous mutations,

Sub-lineages are given the alias of AY.  Delta-AY.1 (Delta with K417N)

Transmissibility compared with wild type

Reproduction number (Ro) ~3.5-5.2*^

Increased transmissibility and secondary attack rate compared with wild type*^

Estimated 43–90% higher reproduction number than wild type and transmission advantage at warmer temperatures *^

Estimated higher rates of transmission in children aged 0 to 9 years. Reports of high seroprevalence rate in secondary school-aged children*^ and some studies inferring an increase in within-school transmission*^

Increased transmissibility and estimated to be 2.5 times greater than wild type*^

Increased transmissibility and secondary attack rate compared with wild type^

Reproduction number (Ro) ranges from 3.2 to 8, with a a mean of 5.0.

Increased transmissibility and secondary attack rate compared with wild type*^ for household and non-household contacts.

Estimated 2.5-fold higher viral loads compared to other variants*^. Similar viral loads between vaccinated and unvaccinated individuals*^

Virological characteristics of vaccine breakthrough infections suggest  Ct-values decreased throughout the first three days of illness*^.  

Data from England suggests a doubling time of 25 days*^. Estimated mean of the latent period and the incubation period are 4.0 days and 5.8 days, respectively*^

Virulence/severity or duration of disease compared with wild type

Increased risk of hospitalisation, possible increased risk of severity and mortality*^

Average infections last 13.3 days compared with 8.2 days for other variants*^ and Alpha does not appear to influence patient trajectories including onset to hospitalisation and length of stay*^

Possible increased risk of severe disease and in-hospital mortality*^

Possible increased risk of hospitalisation and severity of disease *^

Increased risk of emergency care and hospitalisation, including higher odds of oxygen requirement, admission to an intensive care unit, and possible increased risk of mortality*^

Studies show hospitalisation rates for unvaccinated individuals are higher compared with vaccinated individuals*^

Summary of vaccine effectiveness against different outcomes: infection, symptomatic disease, hospitalisation and morality*^. Estimated vaccine effectiveness against hospitalisation and ICU admissions*^ Prior infections result in less severe disease against subsequent infections*^

Resistant against Bamlanivimab*^ and efficiently inhibited by Etesevimab, Imdevimab and by Casirivimab/Imdevimab*^

Some studies suggest symptoms can differ to wild type*^.

Estimated illness duration for children is 5 days, with symptoms including headache and fever*^

Immune escape (vaccines / previous infections will not be protective)
Comirnaty (Pfizer - BNT162b2)

Estimated <2-fold reduction in neutralisation*^

Full vaccination (≥7 days after dose 2) up to 89% vaccine effectiveness against symptomatic infection*^

Vaccine effectiveness profile^*

Estimated 5 to <10-fold reduction in neutralisation*^

Full vaccination (≥7 days after dose 2) up to 84% vaccine effectiveness against symptomatic infection*^

Neutralisation increased with prior COVID-19 infection*^

Vaccine effectiveness profile^*

Estimated 2 to <5-fold reduction in neutralisation

Full vaccination (≥7 days after dose 2) up to 84% vaccine effectiveness against symptomatic infection*^

Neutralisation increased with prior COVID-19 infection*^

Vaccine effectiveness profile^*

Estimated 5 to <10-fold reduction in neutralisation with some studies suggesting an 11.30-fold reduction^*

Full vaccination (≥7 days after dose 2) up to 87% vaccine effectiveness against symptomatic infection^*. Another study suggests  ~90%, ~85% and 79% effectiveness after 30, 60 and 90 days respectively*^

Vaccine effectiveness profile*^

Reported drops in vaccine effectiveness*^ from multiple studies*^, however, there is evidence for the maintenance of protection against severe disease*^ including hospitalisation and mortality*^

Reports suggest a strong effect of waning immunity*^

Reports of phase 3 data show booster (third) dose induces significant neutralising antibody titers*^ with an estimated reduction in relative risk for confirmed infection and severe disease *^

Vaxzevria (AstraZeneca -ChAdOx1))

Estimated 5 to <10-fold reduction in neutralisation*^

Vaccination (≥14 days after dose 1 only) up to 64% vaccine effectiveness against symptomatic infection*^

Vaccine effectiveness profile^* 

Estimated 5 to <10-fold reduction in neutralisation*^

Vaccination (≥14 days after 1 dose only) up to 48% vaccine effectiveness against symptomatic infection*^

Vaccine effectiveness profile^*

Estimated 2 to <5-fold reduction in neutralisation*^

Vaccination (≥14 days after dose 1 only) up to 48% vaccine effectiveness against symptomatic infection*^

Vaccine effectiveness profile

Estimated 2 to <5-fold reduction in neutralisation*^

Vaccination (≥14 days after one dose only) up to 67%  vaccine effectiveness against symptomatic infection*^.  Another study suggests ~69% effectiveness after 14 days after the second dose, and  61% at 90 days*^

Vaccine effectiveness profile*^

Breakthrough infections may cause asymptomatic or mild disease, but are associated with high viral loads, prolonged PCR positivity and low levels of vaccine-induced neutralising antibodies*^

Reported drops in vaccine effectiveness, however, there is evidence for the maintenance of protection against severe disease*^

Spikevac (Moderna -mRNA-1273)

Estimated <2-fold reduction in neutralisation*^

Full vaccination (≥7 days after dose 2) up to 92% vaccine effectiveness against symptomatic infection*^

Vaccine effectiveness profile^*

Estimated 5 to <10-fold reduction in neutralisation*^

Vaccination (≥14 days after dose 1 only) up to 77% vaccine effectiveness against symptomatic infection*^

Vaccine effectiveness profile*^

Estimated 2 to <5-fold reduction in neutralisation*^

Vaccination (≥14 days after dose 1 only) up to 77% vaccine effectiveness against symptomatic infection*^

Vaccine effectiveness profile*^

Estimated 2 to <5-fold reduction in neutralisation*^

Vaccination (≥14 days after dose 1 only) up to 72% vaccine effectiveness against symptomatic infection*^

Reports that two-dose vaccine effectiveness was ~86.7% against Delta infection and ~97.6% against hospitalisation; however, declined with increasing time since vaccination*^

Vaccine effectiveness profile^*

Reported drops in vaccine effectiveness*^ However, there is evidence for the maintenance of protection against severe disease*^

Novavax (NVX-CoV2373)

Estimated  ≥10-fold reduction in neutralisation*^

Vaccine effectiveness profile^*

 Vaccine effectiveness profile*^
Johnson & Johnson (Ad26.COV2.S)

Estimated 2 to <5-fold reduction in neutralisation*^

Vaccine effectiveness profile^*

≥10-fold reduction in neutralisation*^

Vaccine effectiveness profile^*

Estimated 2 to <5-fold reduction in neutralisation*^

Vaccine effectiveness profile^*

Estimated  <2-fold reduction in neutralisation^* 

Vaccine effectiveness profile*^

Immune escape - other

Elicits cross-reactive neutralising antibodies*

Sinovac-CoronaVac: significant reduction in neutralising antibody capacity compared to wild type*^

Reports of breakthrough infections*^

Elicits cross-reactive neutralising antibodies^

Bharat-Covaxin (BBV152): neutralisation with an estimated 3-fold reduction*^

Sinovac-CoronaVac: significant reduction in neutralising antibody capacity compared to wild type*^

Elicits cross-reactive neutralising antibodies^

Sinovac-CoronaVac: estimated <2-fold reduction in neutralisation and a reduction in vaccine effectiveness*^

Cases of reinfection with an estimated 6.4% reinfection probability*^

Transmission is associated with an escape to antibodies targeting non-RBD and RBD Spike epitopes*^

Review of vaccine efficacy, effectiveness and neutralisation data for variants*^

Testing and detection

Limited impact.

S gene target failure; no impact on overall result from multiple target RT-PCR, no impact on Ag RDTs observed.

No impact on RT-PCR or Ag RDTs*^

No reported impacts on diagnostics*^

Lateral flow devices effective in detecting*^ and used as part of the asymptomatic testing program in the UK

Estimated lower PCR Ct values and significantly longer duration of Ct value ≤30 (estimated median duration 18 days for Delta and 13 days for wild-type)*^

Countries reporting detection (not necessarily local transmission) Detected in ~174 countries Detected in ~112 countries Detected in ~72 countries    

Detected in ~154 countries

Current global epidemiology can be characterised by a predominance of Delta.

AY.4 is the dominant lineage in the UK,

The World Health Organization (WHO) announced the Variant naming system on 1 June 2021. The labels do not replace existing scientific names. Designations include Variant of Concern (VOC), Variant of Interest (VOI) and Variants Under Monitoring (VUMs). A previously designated VOC or VOI can also be reclassified if it no longer poses a major added risk to global public health.

Details are tabulated when Variants meet the World Health Organization (WHO) definition of Variant of Concern (VOC).

Reports of Variants of Interest (VOI) are updates identified in the grey literature are below:

Notes

*Preliminary data, not fully established, in some cases small numbers or short follow up; interpret with caution

^ Commentary grey literature, pre-peer review or news

Background

Evidence check - SARS-CoV-2 variants (PDF)

Living evidence tables include some links to low quality sources and an assessment of the original source has not been undertaken. Sources are monitored daily but due to rapidly emerging information, tables may not always reflect the most current evidence. The tables are not peer reviewed, and inclusion does not imply official recommendation nor endorsement of NSW Health.

Last updated on 18 Oct 2021

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