Avidity maturation of anti‐spike IgG after vaccination in COVID‐19 convalescent vs COVID‐19 naïve patients.

Antibodies and avidity maturation contribute to long‐lasting immunity, and previous COVID‐19 seems to enhance the immune response after vaccination. The aim of this study was to compare the immune response after vaccination between COVID‐19 convalescents and naïve patients. Blood samples from COVID‐19 convalescents and naïve patients, taken 1, 3 and 6 months after the second dose of vaccine (mRNA‐vaccine BNT162b2), were analysed for anti‐spike IgG and avidity. Questionnaires concerning side effects were used. Thirty‐one patients in the COVID‐19 cohort and 30 patients in the naïve cohort were included. High levels of anti‐spike IgG and avidity index were seen. Anti‐spike IgG were significantly higher in the COVID‐19 cohort and declining (median 1250, 566, 282 RU/ml vs 565, 187, 65 RU/ml). Avidity did not change over time (median at 6 months 78% vs 65%). The most common side effects were pain at the injection site, malaise and headache. In conclusion, high levels of anti‐spike IgG after vaccination were seen and most patients developed high‐avidity antibodies, although antibody levels and avidity were higher in the COVID‐19 cohort. Over time, the levels of anti‐spike IgG declined, yet avidity remained high. Side effects did not differ between groups and were of short duration. [ABSTRACT FROM AUTHOR]