Timing of detection of immunoglobulin G (IgG), immunoglobulin A (IgA), and immunoglobulin M (IgM) antibodies against severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), and their use to support the diagnosis are of increasing interest. .…Journal of Medical Virology, SARS‐CoV‐2 antibodies: IgA correlates with severity of disease in early COVID‐19 infection, 2021
IgA was the predominant immunoglobulin in early disease and correlated independently with a critical illness. IgG antibodies remained detectable in almost 90% of samples collected up to two months after infection.
The aims of this study were to verify the performance of a newly available commercial antibody assay in patients with PCR‐confirmed COVID‐19 infection on serum samples collected at different time intervals after disease onset and to assess the detection of IgG, IgA, and IgM antibodies according to disease severity.
Source: https://virtualclinic.md/wp-content/uploads/2021/09/8-Journal-of-Medical-Virology-IgA-correlation