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 ). This value was significantly higher with Moderna (18,192 AU ml ) than with Pfizer (10,441 AU ml ). 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 ); in both groups was significantly higher with Moderna than with Pfizer (21,881 vs. 15,733 AU ml and 11,949 vs. 6387 AU ml ), 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 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.