Assessment of Humoral Immune Response to Two Mrna SARS-CoV-2 Vaccines (moderna and Pfizer) in Healthcare Workers Fully Vaccinated with and Without a History of Previous Infection

Aims Presence of anti-S1 region of SARS-CoV-2 spike protein was analysed, at two and eight months, in 477 immunocompetent healthcare workers in Zaragoza, Spain, vaccinated with mRNA-1273 (Moderna) or BNT162b2 (Pfizer). Methods and results Antibody analysis was performed with Alinity i System (Abbott). At 2 months, 100% of vaccinated had anti-S1 IgG (mean = 13,285 AU ml(-1)). This value was significantly higher with Moderna (18,192 AU ml(-1)) than with Pfizer (10,441 AU ml(-1)). The mean value of anti-S1 IgG after vaccination was significantly higher in patients with than without previous infection (18,539 vs. 7919 AU ml(-1)); in both groups was significantly higher with Moderna than with Pfizer (21,881 vs. 15,733 AU ml(-1) and 11,949 vs. 6387 AU ml(-1)), respectively. At 8 months, 100% of patients were IgG positive, with higher levels with Moderna than with Pfizer. Nevertheless, in ensemble of cases, a mean decrease of antibody levels of 11,025 AU ml(-1) was observed. Conclusion At 2 and 8 months after vaccination, IgG response persists with both vaccines but with important decrease which suggests the need for revaccination. Significance and impact of study The study contributes to know the immune status after vaccination with two of more used anti-SARS-CoV-2 vaccines. This knowledge is important for establishing the best vaccination strategy