Evaluation of anti-spike IgG response after inactivated COVID-19 vaccine in healthcare workers

Aim: This study purposed to determine anti-spike IgG levels at the fourth week after the second dose in healthcare workers (HCWs) who had two doses of the CoronaVac vaccine (Sinovac Life Sciences, Beijing, China). The second purpose of the study was to evaluate several factors that may affect antibody levels. 
Material and Method: The study was performed at Kastamonu Training and Research Hospital. A total of 197 HCWs of both genders aged 20-63 were included in this study. Antibody levels that neutralize the SARS-CoV-2 spike protein S1 subunit were determined using the SARS-CoV-2 IgG II Quant kit from serum samples collected from the subjects between 10-16 March 2021. Also, a questionnaire containing information about demographic and clinical data was administered to all subjects. It was statistically investigated whether these data affected the anti-spike IgG levels. 
Results: All subjects had anti-spike IgG levels positive. The median value of the subjects' anti-spike IgG levels was calculated as 860.2 AU/mL (519.1-1674.1 AU/mL). Anti-spike IgG levels were statistically higher in non-smokers and Rh-positive subjects versus the smokers and Rh-negative subjects (p=0.001 and p=0.046, respectively).  However, age groups, gender, COVID-19 history, blood type, and seasonal influenza vaccine did not significantly affect anti-spike IgG levels in the subjects (p>0.05). 
Conclusion: Anti-spike IgG responses were positive in all HCWs who received the CoronaVac vaccine. Besides, the results showed that smoking and Rh-factor affect the anti-spike IgG response. On the other hand, further studies need to examine more parameters with a larger number of subjects.