This study provides useful information about when we can expect antibodies to appear after infection, and how that might be used in future clinical testing.

We are still learning about the antibody response in patients infected with COVID-19 This is a case series of 173 patients with SARS-CoV-2. Serial plasma samples (n=535) were collected during the hospitalizations, and they tested for total antibodies (Ab), IgM and IgG.

The seroconversion rate for Ab (93%), IgM (83%) and IgG (65%) were noted. They thought that the negative antibody findings in 12 patients might be because blood samples were inadequate as illness progressed in a few patients.

The median seroconversion time for Ab, IgM and then IgG were days 11, 12, and 14, respectively. Antibodies were present in <40% of patients within 1-week of onset; by 15 days this had rapidly increased to 100.0% (Ab), 94% (IgM) and 80% (IgG).

In contrast, RNA detectability decreased from 67% in samples collected before day-7 to 46% in days 15-39. Combining RNA and antibody tests significantly improved the sensitivity of pathogenic testing in general for COVID-19.