SARS-CoV-2 Antibody Avidity Responses in COVID-19 Patients and Convalescent Plasma Donors

J Infect Dis. 2020 Nov 13;222(12):1974-1984. doi: 10.1093/infdis/jiaa581.


Background: Convalescent plasma therapy is a leading treatment for conferring temporary immunity to COVID-19-susceptible individuals or for use as post-exposure prophylaxis. However, not all recovered patients develop adequate antibody titers for donation and the relationship between avidity and neutralizing titers is currently not well understood.

Methods: SARS-CoV-2 anti-spike and anti-nucleocapsid IgG titers and avidity were measured in a longitudinal cohort of COVID-19 hospitalized patients (n = 16 individuals) and a cross-sectional sample of convalescent plasma donors (n = 130). Epidemiologic correlates of avidity were examined in donors by linear regression. The association of avidity and a high neutralizing titer (NT) were also assessed in donors using modified Poisson regression.

Results: Antibody avidity increased over duration of infection and remained elevated. In convalescent plasma donors, higher levels of anti-spike avidity were associated with older age, male sex, and hospitalization. Higher NTs had a stronger positive correlation with anti-spike IgG avidity (Spearman ρ = 0.386; P < .001) than with anti-nucleocapsid IgG avidity (Spearman ρ = 0.211; P = .026). Increasing levels of anti-spike IgG avidity were associated with high NT (≥160) (adjusted prevalence ratio = 1.58 [95% confidence interval = 1.19-2.12]), independent of age, sex, and hospitalization.

Conclusions: SARS-CoV-2 antibody avidity correlated with duration of infection and higher neutralizing titers, suggesting a potential alternative screening parameter for identifying optimal convalescent plasma donors.

Keywords: SARS-CoV-2; anti-nucleocapsid; anti-spike; avidity; convalescent plasma.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Antibodies, Neutralizing / administration & dosage*
  • Antibodies, Neutralizing / blood
  • Antibodies, Viral / administration & dosage*
  • Antibodies, Viral / blood
  • Antibody Affinity*
  • Blood Donors
  • COVID-19 / therapy*
  • COVID-19 Serotherapy
  • Cohort Studies
  • Cross-Sectional Studies
  • Female
  • Humans
  • Immunization, Passive
  • Immunoglobulin G / administration & dosage*
  • Immunoglobulin G / blood
  • Linear Models
  • Male
  • Middle Aged
  • SARS-CoV-2*
  • Spike Glycoprotein, Coronavirus / immunology
  • Young Adult


  • Antibodies, Neutralizing
  • Antibodies, Viral
  • Immunoglobulin G
  • Spike Glycoprotein, Coronavirus