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Antiviral Assay for Variants of Concern

Amino acid changes that occur during the virus life cycle have led to the emergence of new coronavirus variants. There are 4 “variants of concern” (Alpha, Beta, Gamma and Delta variants) on the  World Health Organization  (WHO) and the CDC watchlist.  The  “variants of concern” designation is assigned based on increased transmissibility, resistance to  public health measures and/or virulence. The ongoing evolution of SARS-CoV-2 requires continuous research and development to create a  pipeline of effective therapies against COVID-19.

IBT Bioservices offers solutions for research and development challenges to identifying broadly neutralizing candidates to stem the ongoing pandemic. Our recombinant rVSV-SARS-CoV-2 assay can now be used to determine the neutralization potency (IC50 value) of anti-infectives against spike-mediated infectivity of Coronavirus variants of concern.  The platform can evaluate proteins, antibodies, as well as small or large molecules.  If you would like to screen your antiviral candidates, use the form below to contact IBT Bioservices.

Fig. 1. Relative light units (luciferase activity) recorded upon infection of Vero cells using IBT’s rVSV-pseudotype SARS-CoV2 Spike.

                    Fig. 1. Luciferase activity (RLU) in Vero cells infected with rVSV-pseudotype SARS-CoV2 Spike.

Key advantages: The spike protein is a key determinant of host and cell tropism, antigenicity and immunogenicity, interspecies transmission as well as pathogenesis1. These traits make the S protein an attractive target for antiviral inhibitors and vaccines2,3,4. Recombinant VSV pseudotyped with the corona-virus Spike proteins are efficient tools for evaluating mechanisms of virus entry and efficacy of anti-infective  candidates. 

Common Name (Origin)
Pango Lineage
Spike Amino Acid
Parental Strain
(United Kingdom)
del69–70 HV, del144 Y, N501Y, A570D, D614G, P681H, T761I, S982A, D1118H
(South Africa)
K417N, E484K, N501Y, D614G, A701V
Gamma* (Brazil)
L18F, T20N, P26S, D138Y, R190S, K417T, E484K, N501Y, D614G, H655Y, T1027I
Delta* (India)
L452R, E484Q
L452R, D614G
SS13I, W152C, L452R, D614G
D614G (--)



A67V H69del V70del(69) T95I G142D V143del Y144del(143)
Y145del(143) N211del L212I ins214EPE G339D S371L
S373P S375F K417N N440K G446S S477N T478K E484A 
Q493R G496S Q498R N501Y Y505H T547K D614G H655Y 
N679K(674) P681H(674)N764K D796Y N856K Q954H
 N969K L981F



(G75V(77) T76I(77) R246del(245) S247del(245) Y248del(250) L249del(250) T250del
P251del(250) G252del(250) D253N(250) L452Q F490S T547I D614G T859N)
Mu (Colombia)
D614G, D950N, E484K, ins145N, N501Y,e P681H, R346K, T95I, Y144T, Y145S
*Variant of Concern
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Fig. 1 Survival after challenge with INFV H1N1 A/Pert/261/2009 (Tamiflu-resistant strain). Inoculum 1xLD90=1.0E+05 PFU/mouse
Survival after challenge with INFV H1N1 A/Pert/261/2009 (Tamiflu-resistant strain) 1.0E+05 PFU/mouse
Survival and weight change in BALB/c mice challenged with INFV A/ Texas/36/91 (H1N1) and treated with antiviral Osletamivir Phosphate (Tamiflu)
Lung viral load and Survival (30 % weight loss cut-off) in BALB/c mice challenged with INFV H3N2 A/HK/1/68.

Alpha (UK) – B. 1.1.7 / 501Y.V1

amino acid mutations: del69–70 HV, del144 Y, N501Y, A570D, D614G, P681H, T761I, S982A, D1118H

Beta (South Africa) – B.1.351

amino acid mutations: K417N, E484K, N501Y, D614G, A701V

Gamma (Brazil) – P.1

amino acid mutations: L18F, T20N, P26S, D138Y, R190S, K417T, E484K, N501Y, D614G, H655Y, T1027I

Epsilon (Ca, USA) B.1.427

amino acid mutations: L452R, D614G

SARS-CoV-2 Parental Strain Wild Type (Wuhan)
SARS-CoV-2 D614G Variant

amino acid mutations: D614G

Epsilon (Ca, USA) B.1.429

amino acid mutations: S13I, W152C, L452R, D614G

SARS-CoV-2 Delta Variant

amino acid mutations: L452R, E484Q