Biosensor Platform Monitors SARS-CoV-2 Antibody Durability

Low initial severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody titers dropping to undetectable levels within months after infections have raised concerns about long-term immunity.

Seroprevalence studies have begun to show a larger extent of SARS-CoV-2 infections than initially reported because of the high prevalence of infected individuals with mild or no symptoms. However, lower SARS-CoV-2 IgG antibody levels have been reported in those with mild or no symptoms compared with those with severe COVID-19.


A team of Clinical Scientists collaborating with Weill Cornell Medicine (New York, NY, USA) developed a testing-on-a-probe “plus” panel (TOP-Plus) to include a newly developed avidity assay built into the previously described SARS-CoV-2 TOP assays that measured total antibody (TAb), surrogate neutralizing antibody (SNAb), IgM, and IgG on a versatile biosensor platform. TAb and SNAb levels were compared with avidity in previously infected individuals at 5.7 weeks and 30 weeks after infection in paired samples from 80 patients with coronavirus disease 2019 (COVID-19).

Sera from individuals vaccinated for SARS-CoV-2 were also evaluated for antibody avidity. The SARS-CoV-2 TAb and SNAb assays were used to measure plasma TAb and SNAb antibodies against SARS-CoV-2. Plasma samples were assayed on the fully automated Pylon 3-D analyzer (ET HealthCare, Palo Alto, CA, USA). Bio-layer interferometry measurements (Gator Bio, Palo Alto, CA, USA) were used to compare the avidity of 12 different purified COVID-19 antibodies with the TOP-Plus avidity assay.

The investigators reported that the newly designed avidity assay in this TOP panel correlated well with a reference Bio-Layer Interferometry avidity assay. The imprecision of the TOP avidity assay was <10%. Although TAb and neutralization activity (by SNAb) decreased between 5.7 and 30 weeks after infection, the antibody avidity increased significantly. Antibody avidity in 10 SARS-CoV-2 vaccinated individuals (median: 28 days after vaccination) was comparable to the measured antibody avidity in infected individuals (median: 26 days after infection). No cross-reactivity was displayed in sera from patients positive for HIV, Epstein–Barr virus, or rheumatoid factor.

The authors concluded that the TOP-Plus biosensor panel is a versatile sensing platform with high precision and an ability to measure SARS-CoV-2 TAb, SNAb, and individual IgG and IgM antibody levels along with the antibody’s long-term avidity. This combination of all-in-one testing will be a valuable asset in monitoring not only patients convalescing from COVID-19, but also the status of individuals’ COVID-19 vaccination response. The study was published in the September, 2021 issue of the journal Clinical Chemistry.

Related Links:
Weill Cornell Medicine
ET HealthCare
Gator Bio