Research Highlights: Early Development of IgG Antibody in Severe COVID-19 Infection

Concentrations of serum IgG (AU/ml) over time in patients with severe (A, red) and mild (B, blue) disease. Image Source:

Original Article:

  • To accurately interpret COVID-19 surveys related to positive results, it is important to learn the knowledge of serum-IgG responses to COVID-19 virus with a better understanding of patients who do not develop antibody.
  • The research aimed to describe serum-IgG responses to COVID-19 virus in a group of patients with both severe and mild cases of COVID-19.
  • The research includes extended analyses of patients who do not develop specific antibodies for more than 90 days after symptoms begun.
  • SARS-CoV-2-specific IgG antibody levels were quantified using two clinically validated and widely used commercial serological assays.
  • The assays detected antibodies against the spike and nucleocapsid proteins.
  • Forty-seven patients with an average age of 49 years were included.
  • Of all the patients, 38% are female.
  • All patients with severe symptoms and most of the patients with mild symptoms of COVID-19 developed SARS-CoV-2-specific IgG antibodies in serum.
  • The time it takes for the antibody to be detected is significantly shorter in patients with severe compared to mild symptoms.
  • Three patients without detectable IgG-responses after 90 days were observed and all had detectable virus-neutralizing antibodies.
  • From the three patients, two had spike-protein receptor binding domain-specific IgG was detected with an in-house assay.
  • Antibody titers were preserved during follow-up and all patients who developed antibody, regardless of the severity of symptoms, still had detectable IgG levels after 75 days after symptoms begun.
  • Patients with severe COVID-19 both develop antibody earlier and develop higher concentrations of SARS-CoV-2-specific IgG compared to patients with mild symptoms.
  • Patients who not develop detectable IgG antibodies have detectable virus-neutralizing antibodies.
  • The results show that not all COVID-19 patients develop detectable IgG antibody, and are vital for the interpretation of COVID-19 seroprevalence surveys.


Marklund E, Leach S, Axelsson H, Nyström K, Norder H, Bemark M, et al. (2020) Serum-IgG responses to SARS-CoV-2 after mild and severe COVID-19 infection and analysis of IgG non-responders. PLoS ONE 15(10): e0241104.

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