Evaluation of a SARS-CoV-2 Surrogate Virus Neutralization Test for Detection of Antibody in Human, Canine, Cat, and Hamster Sera

Abstract

Surrogate neutralization assays for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that can be done without biosafety level 3 containment and in multiple species are desirable. We evaluate a recently developed surrogate virus neutralization test (sVNT) in comparison to 90% plaque reduction neutralization tests (PRNT₉₀) in human, canine, cat, and hamster sera. With PRNT₉₀ as the reference, sVNT had sensitivity of 98.9% and specificity of 98.8%. Using a panel of immune sera corresponding to other coronaviruses, we confirm the lack of cross-reactivity to other coronaviruses in SARS-CoV-2 sVNT and PRNT₉₀, except for cross-reactivity to SARS-CoV-1 in sVNT.

Keywords: COVID-19; SARS coronavirus 2; SARS-CoV-2; animal; antibody; canine; cat; hamster; human; neutralization; seroepidemiology; serology; surrogate virus neutralization.

FIG 1

Correlation between percent inhibition in the surrogate virus neutralization test (sVNT) and (A) 90% plaque reduction neutralization test (PRNT₉₀) titer or (B) spike RBD ELISA IgG optical density of 205 sera from humans with results confirmed by RT-PCR. (A) Correlation between PRNT₉₀ and percent inhibition in the sVNT. We fitted a linear log regression model between percent inhibition in the sVNT (sVNT_%) and log-transformed PRNT₉₀ titers as follows: ${\text{sVNT}}_{\%}=k_1\times \ln \left[{\log }_2\left(\frac{{\text{PRNT}}_{90}}{10}\right)+2\right]+b_1$. The orange lines indicate estimated percent inhibition, and the orange shading indicates the 95% confidence interval. Blue dots represent the control samples. Black triangles represent samples from confirmed COVID-19 cases obtained less than 10 days since symptom onset, and red diamonds represent samples from confirmed cases obtained 10 days or more after symptom onset. For clarity, the control human sera are not included in the figure as they were negative in all three assays. (B) Correlation between percent inhibition in the sVNT and the spike RBD IgG ELISA optical density. We fitted a linear regression model between percent inhibition in the sVNT and the ELISA OD as follows: ${\text{sVNT}}_{\%}=k_2\times {\text{ELISA}}_{\text{OD}}+b_2$.