Clinical Evaluation of the Abbott Alinity SARS-CoV-2 Spike-Specific Quantitative IgG and IgM Assays among Infected, Recovered, and Vaccinated Groups

The coronavirus disease 19 (COVID-19) pandemic continues to impose a significant burden on global health infrastructure. While identification and containment of new cases remain important, laboratories must now pivot and consider an assessment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunity in the setting of the recent availability of multiple COVID-19 vaccines. Here, we have utilized the latest Abbott Alinity semiquantitative IgM and quantitative IgG spike protein (SP) serology assays (IgM_SP and IgG_SP) in combination with Abbott Alinity IgG nucleocapsid (NC) antibody test (IgG_NC) to assess antibody responses in a cohort of 1,236 unique participants comprised of naive, SARS-CoV-2-infected, and vaccinated (including both naive and recovered) individuals. The IgM_SP and IgG_SP assays were highly specific (100%) with no cross-reactivity to archived samples collected prior to the emergence of SARS-CoV-2, including those from individuals with seasonal coronavirus infections. Clinical sensitivity was 96% after 15 days for both IgM_SP and IgG_SP assays individually. When considered together, the sensitivity was 100%. A combination of NC- and SP-specific serologic assays clearly differentiated naive, SARS-CoV-2-infected, and vaccine-related immune responses. Vaccination resulted in a significant increase in IgG_SP and IgM_SP values, with a major rise in IgG_SP following the booster (second) dose in the naive group. In contrast, SARS-CoV-2-recovered individuals had several-fold higher IgG_SP responses than naive following the primary dose, with a comparatively dampened response following the booster. This work illustrates the strong clinical performance of these new serological assays and their utility in evaluating and distinguishing serological responses to infection and vaccination.