The vast majority of people infected with mild-to-moderate COVID 19 mount a robust antibody response that is relatively stable for at least five months, according to research conducted at the Icahn School of Medicine at Mount Sinai and published, in the journal Science.
Additionally, the research team found that this antibody response correlates with the body’s ability to neutralize (kill) SARS-CoV-2, the virus that causes COVID-19.
Study findings are based on a dataset of 30,082 individuals, who were screened within the Mount Sinai Health System between March and October 2020. The antibody test used in this research—an enzyme-linked immunosorbent assay (ELISA)— is based on the virus’s telltale spike protein that contains the machinery that enables it to attach and gain entry into our cells.
The ELISA assay was developed, validated, and launched at Mount Sinai by a team of internationally renowned researchers and clinicians. The Mount Sinai antibody test detects the presence or absence of antibodies to SARS-CoV-2 and, importantly, is capable of measuring the titer (level) of antibodies an individual has. The high sensitivity and specificity of this test—meaning that a false negative or false positive is highly unlikely—allowed it to be among the first to receive emergency use authorization from New York State and the U.S. Food and Drug Administration.
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—one of the first such programs in the nation. The Clinical Laboratories of The Mount Sinai Hospital set up antibody test results using distinct dilutions set at 1:80, 1:160, 1:320, 1:960 or ≥1:2880. The antibody titer score is generated by the number of times the scientist can dilute a patient’s serum and still be able to detect the presence of antibodies. Titers of 1:80 and 1:160 were categorized as low titers; 1:320 moderate; and 1:960 or ≥ 1:2880 were high.
By early October, Mount Sinai had screened 72,401 individuals with a total of 30,082 being positive (defined as detectible antibodies to the spike protein at a titer of 1:80 or higher). Of the 30,082 positive samples, 690 (2.29 percent) had a titer of 1:80; 1453 (4.83 percent) of 1:160; 6765 (22.49 percent) of 1:320; 9564 (31.79 percent) of 1:960; and 11610 (38.60 percent) of 1:2880. Thus, the vast majority of positive individuals had moderate-to-high titers of anti-spike antibodies.
Another important and outstanding question in the scientific community is the longevity of the antibody response to the spike protein. To answer that question, the team recalled 121 plasma donors at a variety of titer levels for repeat antibody testing at approximately three months and five months post-symptom onset. When comparing overall titers, they saw a slight drop from a geometric mean titer (GMT) of 764 to a GMT of 690 from the first to second testing time point and another drop to a GMT of 404 for the last testing time point, indicating that a moderate level of antibody is retained by most people five months after symptom-onset. In the higher titer range, they observed a slow decline in titer over time. Interestingly, they saw an initial increase in titer for individuals who had originally tested as having low to moderate titer levels. This is in agreement with earlier observations from their study group that indicate seroconversion in mild COVID-19 cases might take a longer time to mount.
The Mount Sinai data reveals antibody binding titers to the spike protein correlate significantly with neutralization of SARS-CoV-2 and that the vast majority of individuals with antibody titers of 320 or higher show neutralizing activity in their serum that are stable over a period of at least 3 months with only modest declines at the five-month time point.
