Rapid evaluation of neutralizing antibodies in COVID-19 patients

To determine whether antibodies produced in response to SARS-CoV-2 infection are protective, a rapid test is needed to evaluate antibody neutralisation capacity in patient plasma. Zhang et al. used ‘Up-conversion phosphor technology-based point-of-care testing’ (UPT-POCT) to quantify total antibodies, and a microneutralisation assay to assess antibody neutralising efficiency, using plasma from both recovered and PCR re-positive COVID-19 patients. UPT-POCT was found to be an effective surrogate marker for neutralising antibody (NAb) activity. This method could be employed for testing vaccine responses, screening convalescent plasma donors and assessing herd immunity. 

Research Highlights

1. Up-conversion phosphor technology-based point-of-care testing (UPT-POCT) uses the RBD of SARS-CoV-2 as the coating protein on the ‘test strip’ and the S1 protein as the UCP-labeling antigen. The test quantifies SARS-CoV-2-specific antibody levels using patient sera. 

2. A positive correlation (correlation coefficient r= 0.9654) was found between T/C ratios reported by UPT-POCT and neutralising antibody (NAb) titres in recovered patient sera samples (519). 

3. Using both re-positive patient sera and recovered patient sera, a correlation between T/C ratio and NAb titres was found, suggesting levels of neutralising antibodies can predict re-infection risk. 

Impact for COVID-19 research:  

• UPT-POCT could be used as a surrogate marker for neutralising antibody capacity to efficiently test vaccine responses, screen convalescent plasma donors and evaluate herd immunity etc. 

Methodologies: 

• Study Type: Cohort study. 

• Key Techniques: Up-conversion phosphor technology-based point-of-care testing (UPT-POCT), microneutralisation assay. 

Limitations: 

• ‘Re-positive’ infection patients not defined clearly. 

• UPT-POCT efficacy was tested against only 1 neutralisation assay. 

• UPT-POCT does not assess IgM or IgA levels, nor antibodies that recognise epitopes outside of the RBD region which could be neutralising. 

• Antibody responses to SARS-CoV-2 may be short lived, and therefore, may not be an efficacious surrogate marker for re-infection.