Circulating IgG levels in SARS-CoV-2 convalescent individuals in Cyprus

Ioannis Mamais, Apostolos Malatras, Gregory Papagregoriou, Natasa Giallourou, Andrea C. Kakouri, Peter Karayiannis, Maria Koliou, Eirini Christaki, Georgios K. Nikolopoulos, Constantinos Deltas

Research output: Contribution to journalArticlepeer-review


Long-term persistence and the heterogeneity of humoral response to SARS-CoV-2 have not yet been thoroughly investigated. The aim of this work is to study the production of circulating immunoglobulin class G (IgG) antibodies against SARS-CoV-2 in individuals with past infection in Cyprus. Individuals of the general population, with or without previous SARS-CoV-2 infection, were invited to visit the Biobank at the Center of Excellence in Biobanking and Biomedical Research of the University of Cyprus. Serum IgG antibodies were measured using the SARS-CoV-2 IgG and the SARS-CoV-2 IgG II Quant assays of Abbott Laboratories. Antibody responses to SARS-CoV-2 were also evaluated against participants’ demographic and clinical data. All statistical analyses were conducted in Stata 16. The median levels of receptor binding domain (RBD)-specific IgG in 969 unvaccinated individuals, who were reportedly infected between November 2020 and September 2021, were 432.1 arbitrary units (AI)/mL (interquartile range—IQR: 182.4–1147.3). Higher antibody levels were observed in older participants, males, and those who reportedly developed symptoms or were hospitalized. The RBD-specific IgG levels peaked at three months post symptom onset and subsequently decreased up to month six, with a slower decay thereafter. IgG response to the RBD of SARS-CoV-2 is bi-phasic with considerable titer variability. Levels of IgG are significantly associated with several parameters, including age, gender, and severity of symptoms.

Original languageEnglish
Article number5882
JournalJournal of Clinical Medicine
Issue number24
Publication statusPublished - 1 Dec 2021
Externally publishedYes


  • Antibodies
  • COVID-19
  • Cyprus
  • IgG
  • SARS-CoV-2


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