SARS‐CoV‐2 antibodies: IgA correlates with severity of disease in early COVID‐19 infection

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. We used the Gold Standard Diagnostics ELISA to evaluate the kinetics of SARS‐CoV‐2 IgG, IgA, and IgM antibodies in sera of 82 hospitalized patients with polymerase chain reaction (PCR)‐confirmed coronavirus disease 2019 (COVID‐19). Serum samples were collected 1–59 days post‐onset of symptoms (PoS) and we examined the association of age, sex, disease severity, and symptoms' duration with antibody levels. We also tested sera of 100 ambulatory hospital employees with PCR‐confirmed COVID‐19 and samples collected during convalescence, 35–57 days PoS. All but four of the admitted patients (95.1%) developed antibodies to SARS‐CoV‐2. Antibodies were detected within 7 days PoS; IgA in 60.0%, IgM in 53.3%, and IgG in 46.7% of samples. IgG positivity increased to 100% on Day 21. We did not observe significant differences in the rate of antibody development in regard to age and sex. IgA levels were highest in patients with a severe and critical illness. In multiple regression analyses, only IgA levels were statistically significantly correlated with critical disease (p = .05) regardless of age, sex, and duration of symptoms. Among 100 ambulatory hospital employees who had antibody testing after 4 weeks PoS only 10% had positive IgA antibodies. The most frequently isolated isotype in sera of employees after 30 days PoS was IgG (88%). 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. Highlights IgA was the predominant immunoglobulin detected in early COVID‐19 disease. IgA levels were highest in patients with a severe and critical illness. IgG antibodies remained detectable in almost 90% of samples collected up to 2 months after infection.