SARS-CoV-2 IgG Spike antibody levels and avidity in natural infection or following vaccination with mRNA-1273 or BNT162b2 vaccines.

Certain aspects of the immunogenicity and effectiveness of the messenger ribonucleic acid (mRNA) vaccines (mRNA-1273 and BNT162b2) developed in response to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic are still uncharacterized. Serum or plasma samples from healthy donor recipients of either vaccine (BNT162b2  = 53, mRNA-1273  = 49; age 23-67), and individuals naturally infected with SARS-CoV-2 ( = 106; age 18-82) were collected 0-2 months post-infection or 1- and 4 months after second dose of vaccination. Anti-Spike antibody levels and avidity were measured via an enzyme-linked immunosorbent assay (ELISA). Overall, vaccination induced higher circulating anti-Spike protein immunoglobulin G (IgG) antibody levels and avidity compared to infection at similar time intervals. Both vaccines produced similar anti-Spike IgG concentrations at 1 month, while mRNA-1273 demonstrated significantly higher circulating antibody concentrations after 4 months. mRNA-1273 induced significantly higher avidity at month 1 compared to BNT162b2 across all age groups. However, the 23-34 age group was the only group to maintain statistical significance by 4 months. Male BNT162b2 recipients were approaching statistically significant lower anti-Spike IgG avidity compared to females by month 4. These findings demonstrate enhanced anti-Spike IgG levels and avidity following vaccination compared to natural infection. In addition, the mRNA-1273 vaccine induced higher antibody levels by 4 months compared to BNT162b2.