SARS-CoV-2 Neutralizing Antibody
Mount Sinai Health System was one of the first laboratories to develop a quantitative enzyme linked immunosorbent assay (ELISA) that detected antibody to the SARS-CoV-2 spike protein and receive emergency use authorization from both New York State and the FDA.
In late March, Mount Sinai began to screen people for antibodies to SARS-CoV-2 in order to recruit volunteer donors for its convalescent plasma therapy program. Patient sera were tested at dilutions of 1:80, 1:160, 1:320, 1:960 or ≥1:2880. Titers of 1:80 and 1:160 were considered to be low titers; while 1:320 were considered to be moderate; and 1:960 or ≥ 1:2880 were high.
By early October, Mount Sinai had screened 72,401 individuals. A total of 30,082 individuals were seropositive, having detectable antibodies to the spike protein at a titer of 1:80 or higher. Of the 30,082 positive samples, 690 (2.29%) had a titer of 1:80; 1453 (4.83%) of 1:160; 6765 (22.49%) of 1:320; 9564 (31.79%) of 1:960; and 11,610 (38.60% of 1:2880. Most positive individuals had moderate-to-high titers of anti-spike antibodies.
The Mount Sinai team also investigated the duration of the antibody response to the spike protein by testing 121 convalescent plasma donors with a variety of antibody titers at approximately three months and five months post-symptom onset. Overall, there was a slight drop in antibody level from a geometric mean titer (GMT) of 764 to a GMT of 690 after three months and another drop to a GMT of 404 after five months. Most patients maintained a moderate level of antibody at five months after symptom-onset.
Lastly, the research team tested 120 samples with titers ranging from negative to >1:2880 with a quantitative microneutralization assay using SARS-CoV-2 virus. Approximately 50% of sera with titers of 1:80 to 1:160 had neutralizing activity; 90% with titers in the 1:320 range had neutralizing activity; and all sera in the 1:960 to ≥1:2880 range had neutralizing activity. Furthermore, neutralizing activity against SARS-CoV-2 virus was stable for at least 3 months and showed modest declines at five months.
This study revealed that the titer of antibody directed against the spike protein correlated significantly with neutralization of SARS-CoV-2 virus and that most individuals with antibody titers of 320 or higher maintained stable neutralizing activity for at least 3 months with only modest declines by 5 months.
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