During preliminary studies of a competitive enzyme linked immunoassay (Comp EIA), utilising a labelled neutralising monoclonal antibody binding to solid-phase receptor binding domain (RBD) to detect and characterise antibody to RBD (anti-RBD), we compared the performance of post-infection and post-immunisation serological responses in the human host. In a Comp EIA the degree of inhibition can range from total ablation of label binding (100% inhibition) to an absence of detectable inhibition (0% inhibition). The avidity with which an antibody binds the target RBD will determine its inhibitory efficiency. The greater the avidity the greater is its displayed inhibition and vice versa.
We collected sera from recovery patients, taken up to 32 weeks from illness onset and from immunised persons, taken between 14 and 30 days after a second dose of vaccine and compared the inhibition displayed in the Comp EIA with the level of total anti-RBD detected in the Imperial hybrid double antigen binding assay (DABA). The level of inhibition displayed by the antibody generated by infection and by vaccine differs markedly (Figure 1a), despite both sets of samples displaying similar levels of anti-RBD (Figure 1b). Post-recovery antibody appears to be ineffectual in its ability to react strongly with RBD epitopes but is “hardened” by a single dose of vaccine (Figure 1b).
This is the first time this disparity has been shown and constitutes a salutary warning to those who would espouse an anti-vaccine philosophy. The implications of this observation are two-fold. Firstly, natural immunity is unlikely to impact on transmissibility of SARS CoV 2 both in the population and in health-care settings. Secondly, it highlights a need for stringent selection of donors of convalescent plasma for therapy1,2 and the need to consider post-recovery vaccine immunisation prior to plasma collection.
In essence, our data serve to underline graphically the importance of wide-spread immunisation of the UK population with vaccines for the control of this virus, rather than relying only on the concept of natural infection or herd immunity protection, especially in health-care settings.