Commercial immunoassays for detection of anti-SARS-CoV-2 spike and RBD antibodies: urgent call for validation against new and highly mutated variants.

Measuring the level of protection conferred by anti-SARS-CoV-2 (trimeric) spike or RBD (receptor binding domain) antibodies (especially total and IgG) is a suitable and reliable approach for predicting biological protection against the risk of infection and severe coronavirus disease 2019 (COVID-19) illness. Nonetheless, SARS-CoV-2 has undergone a broad process of recombination since the identification of the prototype lineage in 2019, introducing a huge number of mutations in its genome and generating a vast array of variants of interest (VoI) and concern (VoC). Many of such variants developed several mutations in spike protein and RBD, with the new Omicron (B.1.1.529) clade displaying over 30 changes, 15 of which concentrated in the RBD. Besides their impact on virus biology, as well as on the risk of detection failure with some molecular techniques (i.e., S gene dropout), recent evidence suggests that these mutations may also jeopardize the reliability of currently available commercial immunoassays for detecting anti-SARS-CoV-2 antibodies. The antigen (either spike or RBD) and epitopes of the prototype SARS-CoV-2 coated in some immunoassays may no longer reflect the sequence of circulating variants. On the other hand, anti-SARS-CoV-2 antibodies elicited by highly mutated SARS-CoV-2 variants may no longer be efficiently recognized by the currently available commercial immunoassays. Therefore, beside the compelling need to regularly re-evaluate and revalidate all commercially available immunoassays against live virus neutralization assays based on emerging VoCs or VoIs, diagnostic companies may also consider to redevelop their methods, replacing former SARS-CoV-2 antigens and epitopes with those of the new variants.