[Humoral immunity against SARS-CoV-2 in workers of social health care centers of Castilla y León after vaccination with the BNT162b2 mRNA vaccine from Pfizer/Biontech.].

OBJECTIVE

Workers and residents of care facilities for elder people/people with disabilities were particularly hit by the COVID-19 pandemic. Workers from these centres were included as a priority group for vaccination against SARS-CoV-2. The Family Ministry of Castilla y León realized a seroprevalence survey measuring the humoral immunity of its workers after the vaccination against SARS-CoV-2.

METHODS

In February and March 2021, IgM/IgG antibodies were measured in 7 social health care centers in a total of 1,085 workers at least 15 days after completing the vaccination with the BNT162b2 vaccine from Pfizer/BioNtech. Using the ELISA technique for anti-nucleocapsid (N) IgM and CLIA S-RBD SARS-CoV-2 for anti-spicule (S) IgG, titers were compared between vaccinated with cero, one or two doses, and differentiating in these subgroups between having passed or not COVID-19. Means and percentages were compared using Student's t and Chi2 (EPIDAT 3.1).

RESULTS

Among the 1,085 workers studied, there were 54 workers with a single dose of vaccine, of which 51 (94%) had a positive IgG (average titers of 459 AU/mL), 951 workers with 2 doses, of which 949 (99.8%) showed positive IgG (mean titers of 677 AU/mL), and 80 unvaccinated workers, of which 51 (64%) had positve IgG (mean titers of 49 AU/mL). 7 cases of COVID-19 were notified at least 15 days after full vaccination. The titers were significantly higher if COVID-19 had been passed in the group vaccinated with 1 and 2 doses (259 vs 894 and 601 vs 1,085 AU/mL respectively, p<0.05), but not in the unvaccinated group (53 vs 34 AU/mL, p<0.05).

CONCLUSIONS

99.8% of social health workers who received 2 doses of the BNT162b2 vaccine from Pfizer/BioNtech, and 94% of those who received 1 single dose, presented humoral immunity with high IgG titers, with high clinical effectiveness expressed in the absence of cases. 64% of unvaccinated workers presented humoral immunity. The history of having passed COVID-19 produces an important booster effect both after one and after two doses of vaccine. Measurement of humoral immunity against SARS-CoV-2 could be considered as a parameter for sufficient immunity.