Introduction

Since the appearance of the first cases of COVID-19, the pandemic has shown rapid growth with an impact on a global scale. The ability to generate immunity is a key factor for its control, which is why it has been a topic of exhaustive scientific investigation so far. However, despite the widespread administration of vaccines, several doubts remain as to their immunogenicity.

The literature suggests that age, gender, and previous serological status influence the difference in humoral immune response. Seropositivity, young age and female gender seem to have a positive influence on antibody levels in most studies published so far.

Objectives

The aim of this study is to evaluate the humoral response to the Pfizer-BionNTech vaccine in healthcare professionals at a hospital.

Methods

Professionals with both positive and negative serology were inoculated with two doses. The influence of age, gender and previous serological status on antibody levels was analyzed over a period of six months.

Antibodies were assayed using Abbott's SARS-CoV-2 IgG chemiluminescence immunoassay (SARS-CoV-2 IgG II Quant®) in four stages: prior to the first vaccine inoculation, as well as on the first, third and sixth month after the second inoculation.

The study included an initial sample of 1387 health professionals, but only 391 strictly complied with the 4 stages mentioned above. Of the final sample of 391 collaborators, 341 had negative serology prior to vaccination, and had no history of positive RT-PCR for COVID-19. The remaining 50 had positive serology (>6.8 AU/mL).

Results

It is observed that there is a more robust response in previously seropositive individuals, having presented a higher quantitative value of IgG, but with a similar behaviour to seronegatives regarding sustainability. Antibodies peaked in the first month, especially in younger subjects, showing a progressive decline in the post-vaccination semester for both groups. In a population where the female sex is predominant, it was this one that had a more robust quantitative response to IgG. Finally, we found a marked decrease in the number of symptomatic infections by COVID-19 after immunization, which is transversal to all the current literature.

Conclusion

In summary, we conclude that previously infected individuals vaccinated with two doses have the same serological behavior regarding humoral immunity compared to uninfected individuals vaccinated with two doses. This result reinforces that the humoral immunity assay cannot be utilized as a clinical tool for the selection and prioritization of whom to vaccinate.

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