Temporal correlations between RBD-ACE2 blocking and binding antibodies to SARS-CoV-2 variants in CoronaVac-vaccinated individuals and their persistence in COVID-19 patients

Abstract

Antibodies play a crucial role in protection against SARS-CoV-2. Understanding the correlation between binding and functional antibodies is essential to determine whether binding antibody levels can reliably predict neutralizing activity. We assessed antibody responses in 111 individuals vaccinated with the inactivated vaccine CoronaVac and 111 COVID-19 patients in Thailand. Plasma levels of ACE2-blocking antibodies targeting the receptor-binding domain (RBD) of SARS-Co-V2 variants were measured before vaccination and at 14 and 28 days after the second dose using a multiplex surrogate virus neutralization test. Anti-spike and anti-nucleocapsid antibodies were quantified by electrochemiluminescence immunoassay, and anti-RBD IgG by ELISA. After vaccination, blocking, anti-spike, and IgG antibody levels increased but declined rapidly within a month, whereas antibody levels in COVID-19 patients increased and persisted. Blocking and anti-spike antibody correlated at day 14 post-vaccination but not at day 28. In COVID-19 patients, correlations were moderate at day 14, and stronger at day 28. Correlations were weaker for Omicron subvariants than for the ancestral strain and non-Omicron variants. The weak correlation between blocking and anti-RBD IgG suggests binding antibodies might not predict neutralizing activity. These findings highlight the temporal nature of CoronaVac-induced immunity and the need for booster doses and variant-adapted vaccine.

Keywords: Anti-spike antibody; COVID-19; Correlation; RBD-ACE2 blocking antibody; SARS-CoV-2; Vaccine.

Fig. 1

Timeline of sample collections and dominant circulating variants during the study period (A) and study flow diagram (B). This prospective study enrolled 111 CoronaVac-vaccinated individuals from May to June 2021 and 111 COVID-19 patients from three hospitals in central Thailand from July 2021 to December 2022^,. Plasma samples were collected on days 0, 14, and 28. RBD-ACE2 blocking antibody levels against the SARS-CoV-2 ancestral strain and 12 variants were assessed using multiplex sVNT. Anti-spike antibody levels were measured using ECLIA, and anti-RBD IgG antibodies specific to the SARS-CoV-2 RBD of the Delta variant were determined by ELISA.

Fig. 2

RBD-ACE2 blocking antibody (A), anti-spike antibody (B), and anti-RBD IgG antibody levels (C) in CoronaVac-vaccinated individuals. Blocking antibodies against ancestral SARS-CoV-2 and 12 non-Omicron and Omicron variants were determined using multiplex sVNT assay. Anti-spike antibodies were measured using the Elecsys^® anti-spike assay, and anti-RBD IgG antibodies against RBD of the Delta variant were determined using in-house ELISA. A negative result for nAbs was defined as a percent inhibition lower than 30% (indicated by the dotted red line), whereas a negative result for anti-spike antibodies was defined a level lower than 0.8 U/ml. The Kruksall-Wallis test with Dunn’s multiple comparison test was used to assess differences between groups. Data of anti-RBD IgG levels were obtained from.

Fig. 3

RBD-ACE2 blocking antibody (A), anti-spike antibody (B), and anti-RBD IgG antibody levels (C) in COVID-19 patients. Blocking antibodies against ancestral SARS-CoV-2 and 12 non-Omicron and Omicron variants were detected by multiplex sVNT, anti-spike antibodies were detected by the Elecsys^® anti-spike assay, and anti-RBD IgG antibodies against SARS-CoV-2 RBD of the Delta variant were detected by ELISA. A negative result for nAbs was defined as a percent inhibition lower than 30% (indicated by the dotted red line), whereas a negative result for anti-spike antibodies was defined levels lower than 0.8 U/ml. The Kruksall-Wallis test with Dunn’s multiple comparison test was used to assess differences between the groups. Data of nAb and anti-RBD IgG levels were obtained from^,.

Fig. 4

Correlation between RBD-ACE2 blocking and anti-spike antibody levels on day 14 in CoronaVac-vaccinated individuals. Blocking antibodies were detected using the sVNT assay, and anti-spike antibodies were detected using the Elecsys® anti-spike assay. The pairwise correlation coefficient (r) was determined using Spearman’s rank correlation.

Fig. 5

Correlations between RBD-ACE2 blocking and anti-spike antibody levels on day 28 in CoronaVac-vaccinated individuals. Blocking antibodies were detected using the sVNT assay, and anti-spike antibodies were detected using the Elecsys^® anti-spike assay. The pairwise correlation coefficient (r) was determined using Spearman’s rank correlation.

Fig. 6

Correlation between RBD-ACE2 blocking and anti-spike antibody levels on day 14 in patients with COVID-19. Blocking antibodies were detected by the sVNT assay, whereas anti-spike antibodies were measured using the Elecsys® anti-spike assay. The pairwise correlation coefficient (r) was determined using Spearman’s rank correlation.

Fig. 7

Correlation between RBD-ACE2 blocking and anti-spike antibody levels on day 28 in patients with COVID-19. Blocking antibodies were detected using the sVNT assay, whereas anti-spike antibodies were measured using the Elecsys^® anti-spike assay. The pairwise correlation coefficient (r) was determined using Spearman’s rank correlation.

Fig. 8

Correlation between anti-spike and anti-RBD IgG antibody levels on days 14 and 28 in CoronaVac-vaccinated individuals (A and B) and patients with COVID-19 (C and D). Anti-spike antibodies were detected using the Elecsys® anti-spike assay, and anti-RBD IgG antibodies against the SARS-CoV-2 Delta variant were measured using ELISA^,. The pairwise correlation coefficient (r) was determined using Spearman’s rank correlation.