Comparison of an inactivated Covid19 vaccine-induced antibody response with concurrent natural Covid19 infection.

Objectives: The risk of contracting SARS-CoV-2 is high among the health care workers (HCW). The comparison between the antibody response to an inactivated Covid19 vaccine and the antibodies that developed during Covid-19 infection has not been elucidated. In this study, vaccine-induced antibody levels were compared with the antibodies developed in naturally infected HCWs.

Methods: Eighty vaccinated individuals and 80 Covid-19 patients enrolled to the study. Both groups were matched on age, gender and antibody testing time. Anti-SARS-CoV-2 total Ig (Roche) and Anti-SARS-CoV-2 ELISA (IgG) (Euroimmun, Germany) were used to detect antibodies.

Results: The anti-S positivity were determined to be 96.2% and 92.5% in vaccinated and patient groups (p=0.303) while the anti-N positivity was 51.2% and 98.8%, respectively (p=<0,0001). The median values for anti-S and anti-N antibodies were statistically significant between both groups. When the vaccinated group was compared with the severe and non-severe patient groups, statistically significant differences were found for both regarding anti-S1 and anti-N antibody titers (p=0,012, p=<0,0001, respectively). For the patient group, there was a positive correlation between the age and anti-S1 antibody titers (r=0.333; p=0.003) and there was also a statistically significant increase in anti-N antibody titers in time (r=0.505; p=0.0001).

Conclusion: The anti-S seroconversion ratio in vaccinated individuals were higher than what was reported by the vaccine manufacturer. The antibody titers in the vaccinated group were lower than the patients group. The decrease in anti-S1 antibody titers in time were considered to be a disadvantage and an undesired phenomenon.