Evaluation the correlation between anti-spike protein IgG antibody
titers against SARS-CoV-2 Prototype and different Omicron variants by
ELISA and neutralization activity
Abstract
Evaluating the IgG titers targeting the S protein of SARS-CoV-2 by ELISA
assays have been used in the development of several anti-SARS-CoV-2
vaccines in China. It is unclear whether the IgG levels against S
protein tested by ELISA can monitor immune evasion against different
Omicron variants. In the study, 88 recipients immunized with three doses
of a COVID-19-inactivated vaccine were enrolled, whose serum samples
were collected within 2 months after the third immunization. The IgG
antibody levels were detected by using three commercial ELISA kits,
which coated the S protein of the prototype, Omicron BA.1 and BA.5
variants respectively. The neutralizing activities of sera against the
pseudotyped Omicron variant, prototype was determined. We also analyzed
the correlation between the IgG titers with the neutralizing antibodies.
The results showed that, after the third dose of the homologous
inactivated vaccine, the neutralizing activity against the Omicron
variant BA.1(GMT, 60) and BA. 5(GMT, 42) were decreased significantly
compared with the prototype (GMT, 331) respectively (
P<0.05). However, the IgG titers against the S of
Omicron BA.1(GMT, 2334) and BA.5(GMT, 2447) variants showed no
significant difference with the prototype (GMT, 2797). Our results
showed different correlation levels between anti-Spike protein of
SARS-CoV-2 IgG titers and neutralizing antibodies, against SARS-CoV-2
prototype, Omicron variant BA.1 and BA.5 In summary, our result
highlight that the Omicron variant BA.1 and BA.5 escape vaccine-induced
immunity by neutralization activity test, and IgG titers against the
SARS-CoV-2 Spike protein can not predict the viral immune evasion
against different Omicron variants.