2 Interpreting and reporting results

The results from this type of ELISA are usually reported as the reciprocal of the highest dilution that shows a positive result. For example, if the highest dilution giving a positive result is 1:64, then the titre would be reported as 64. This has the advantage that a larger number indicates a greater amount of antibody in the serum.

It should be emphasized that the type of ELISA that has been taught here is not highly accurate. If your results are out by one well, then you would report a value that is different by a factor of two from the stated value. The advantage of this assay is not in its accuracy, but in its speed and simplicity. It gives a rapid estimation of whether antibodies to the test antigen are present in significant amounts. As such it is very good for screening large numbers of samples in epidemiological studies.

The results of the ELISA you carried out, show that four individuals (N9921, C5050, H1151, Z8207) had significant levels of antibodies to spike protein. (The low titre in C4443 is more likely due to a high background value in the assay rather than evidence of contact with SARS-CoV2 spike protein.)

Finally, it is important to emphasize that the four positive samples do not necessarily imply that those four individuals have been infected with SARS-CoV2. Vaccination against COVID-19 also induces antibodies to spike protein, so we can say that these individuals have been vaccinated or infected, or possibly both.