SARS-CoV-2 Serologic Assays in Control and Unknown Populations Demonstrate the Necessity of Virus Neutralization Testing

Rathe, Jennifer A; Hemann, Emily A; Eggenberger, Julie; Li, Zhaoqi; Knoll, Megan L; Stokes, Caleb; Hsiang, Tien-Ying; Netland, Jason; Takehara, Kennidy K; Pepper, Marion; Gale, Michael

BACKGROUND: To determine how serologic antibody testing outcome links with virus neutralization of SARS-CoV-2, we evaluated a unique set of individuals for SARS-CoV-2 antibody level and viral neutralization. METHODS: We compared serum Ig levels across platforms of viral antigens and antibodies with 15 positive and 30 negative SARS-CoV-2 controls followed by viral neutralization assessment. We then applied these platforms to a clinically relevant cohort of 114 individuals with unknown histories of SARS-CoV-2 infection. RESULTS: In controls, the best performing virus-specific antibody detection platforms were SARS-CoV-2 receptor binding domain (RBD) IgG [specificity 87%, sensitivity 100%, positive predictive value (PPV) 100%, negative predictive value (NPV) 93%], spike IgG3 [specificity 93%, sensitivity 97%, PPV 93%, NPV 97%], and nucleocapsid protein (NP) IgG [specificity 93%, sensitivity 97%, PPV 93%, NPV 97%]. Neutralization of positive and negative control sera showed 100% agreement. 20 unknown individuals had detectable SARS-CoV-2 antibodies with 16 demonstrating virus neutralization. Spike IgG3 provided the highest accuracy for predicting serologically positive individuals with virus neutralization activity [Misidentified 1/20 unknowns compared to 2/20 for RBD and NP IgG]. CONCLUSION: The coupling of virus neutralization analysis to a spike IgG3 antibody test is optimal to categorize patients for correlates of SARS-CoV-2 immune protection status.