Evaluation of the Antibody Response Induced by the Pfizer-BioNTech COVID-19 Vaccine and the Effect Prior COVID-19 Infection has on the Response Elicited by the Vaccine.

Introduction Understanding the immune memory of individuals who have naturally contracted SARS CoV-2 versus naïve individuals might help to optimise the vaccination campaigns. Here we describe the Anti-SARS-CoV-2 IgG response induced by the Pfizer-BioNTech COVID-19 Vaccine in both naive individuals and those with prior confirmed SARS-CoV-2 infection. We also look at the durability of that response over a six-month period. Methods This study enrolled a total of 219 participants who had completed the full course of the Pfizer BioNTech BNT162b1 COVID 19 vaccine. SARS CoV-2 IgG levels were measured at two different stages over a period of six months using Abbott Architect SARS-CoV-2 IgG II quantitative assay. Results After two doses of the Pfizer BioNTech BNT162b1 COVID 19 vaccine, the median SARS CoV-2 IgG concentration from all participants was 4866 AU/mL (IQR 2738-8424). Median IgG levels in naïve individuals were 4219 AU/mL (IQR 2450-7602). Median SARS CoV-2 IgG levels were significantly higher in those with a previous SARS CoV-2 infection at 8323 AU/mL (IQR 4728-16579 p<0.001). Median SARS-CoV-2 IgG levels decreased to 953 AU/mL (IQR 512-1730) after six months post vaccination. This represented a median decrease of 80% between the two testing periods Conclusion Our findings suggest that those with natural infection before vaccination produce a higher IgG response than naïve individuals as shown by a nearly 2-fold increase in the mean concentrations between the two groups.SARS-CoV-2 IgG levels showed a median decline of 2% per day.