Virus Neutralization Assay Results
To determine whether serum samples in which SARS-CoV-2 antigen-specific
IgG was detected were able to neutralize SARS-CoV-2, we performed a
live-virus neutralization assay. We selected samples from four
categories, which were determined based on the corresponding ELISA
results: I. Positive for SARS-CoV-2- and IBV-specific IgG (comprised of
10 vaccine implementers and one poultry worker); II. Positive for
SARS-CoV-2-specific IgG (comprised of four COVID-19 patients and one
vaccine implementer); III. Negative for SARS-CoV-2- and IBV-specific IgG
(comprised of one vaccine implementer, two poultry workers, and one
pre-pandemic control); IV. Negative for SARS-CoV-2-specific IgG and
positive for IBV-specific IgG (comprised of two vaccine implementers).
The IgG ratios of samples from each group are presented in Figure S7A.
Only samples from group II (antibody-positive group against SARS-CoV-2)
were able to neutralize in vitro SARS-CoV-2-mediated killing of
Vero E6 cells. The geometric mean of neutralization titers were 1:16, 1:
35.78, 1: 80, 1: 16, and 1: 80 for VI17, C12, C13, C14, and C16,
respectively (Table 1). Representative examples of positive, negative,
and poultry farm personnel serum samples are shown in Figure S7B.