It takes time to develop an immune response with the development of antibodies. Generally, most people form antibodies except those who are either immunocompromised or IgG deficient. Testing too soon will lead to a negative antibody test result. There is insufficient scientific information to understand the variation of timing and amount of antibody that develops to the SARS-CoV-2 virus that can be applied to all patients. Yet, we have experience with other viruses and can apply these learnings to SARS-CoV-2 until we know more.
Studies have begun measuring the seroconversion in SARS-CoV-2 patients. In one such study, 173 hospitalized patients in China, all patients (100%) developed antibodies against SARS-CoV-2.1 The median time to have detectable antibodies (called seroconversion) was 11 to 14 days, depending upon the type of immunoglobulin. (The median time is the number of days when 50% of those tested positive after the onset of symptoms.) 94% and 80% demonstrated seroconversion with IgM and IgG, respectively, by day 15 after the onset of symptoms. This study provides information from a small number of patients; larger studies are needed.
Findings from an antibody study of patients infected with a related virus to SARS-CoV-2 (namely the SARS-CoV outbreak in 2002-2003) demonstrated that among 176 patients who had severe acute respiratory syndrome, SARS-specific antibodies were maintained for an average of 2 years, and significant reduction of immunoglobulin G–positive percentage and titers occurred in the third year.2