Marked increase in avidity of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) antibodies 7-8 months after infection is not diminished in old age.

The kinetics of IgG avidity maturation during severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection obtained from 217 participants of the Ischgl cohort, Austria, was studied 0.5-1.5 (baseline) and 7-8 months (follow up) after infection. The IgG avidity assay, using a modified IgG ELISA and 5.5 M urea, revealed that old age does not diminish the increase in avidity, detected in all participants positive at both time points, from 18% to 42%. High avidity was associated with a marked residual neutralization capacity in 97.2.% of participants (211/217), which was even higher in the older age group, revealing an important role of avidity assays as easy and cheap surrogate tests for assessing the maturation of the immune system conveying potential protection against further SARS-CoV-2 infections without necessitating expensive and laborious neutralization assays.