Correlations between three ELISA protocols measurements of RTS,S/AS01-induced anti-CSP IgG antibodies

PLoS One. 2023 May 23;18(5):e0286117. doi: 10.1371/journal.pone.0286117. eCollection 2023.


Background: RTS,S/AS01 induced anti-circumsporozoite protein (CSP) IgG antibodies are associated with the vaccine efficacy. There is currently no international standardisation of the assays used in the measurement of anti-CSP IgG antibody concentrations for use in evaluations of the vaccine's immunogenicity and/or efficacy. Here, we compared the levels of RTS,S/AS01 induced anti-CSP IgG antibodies measured using three different enzyme-Linked ImmunoSorbent Assays (ELISA).

Methods: 196 plasma samples were randomly selected from the 447 samples collected during the RTS,S/AS01 phase IIb trial in 2007 from Kenyan children aged between 5-17 months. The vaccine-induced anti-CSP IgG antibodies were then measured using two independently developed ELISA protocols ('Kilifi-RTS,S' and 'Oxford-R21') and compared to the results from the reference 'Ghent-RTS,S' protocol for the same participants. For each pair of protocols, a deming regression model was fitted. Linear equations were then derived to aid in conversions into equivalent ELISA units. The agreement was assessed using Bland and Altman method.

Findings: The anti-CSP IgG antibodies measured from the three ELISA protocols were in agreement, and were positively and linearly correlated; 'Oxford' and 'Kilifi' r = 0.93 (95% CI 0.91-0.95), 'Oxford' and 'Ghent' r = 0.94 (95% CI: 0.92-0.96), and 'Kilifi' and 'Ghent' r = 0.97 (95% CI: 0.96-0.98), p<0.0001 for all correlations.

Conclusions: With the linearity, agreement and correlations established between the assays, conversion equations can be applied to convert results into equivalent units, enabling comparisons of immunogenicities across different vaccines of the same CSP antigens. This study highlights the need for the international harmonisation of anti-CSP antibody measurements.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Enzyme-Linked Immunosorbent Assay* / methods
  • Humans
  • Immunoglobulin G* / analysis
  • Infant
  • Kenya


  • Immunoglobulin G

Grants and funding

“FMN was supported by an MRC/UKAID African Research Leadership Award (MR/P020321/1), a Senior Fellowship from EDCTP (TMA2016SF-1513), and the samples were collected within the Kilifi immunology cohorts supported by PATH Malaria Vaccine Initiative (MVI) and the Wellcome Trust (grants 073597; 061702; 077176)”. KJE is funded by a fellowship from the Calleva Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.