Antibody response to receptor-binding domain of SARS-CoV-2 spike protein following vaccination and natural infection with SARS-CoV-2

Background and objectives: Antibody to SARS-CoV-2 develops both after natural infection with SARS-CoV-2 and vaccination. This study was undertaken to determine the antibody response to SARS-CoV-2 among population after natural SARS-CoV-2 infection and vaccination. Material and methods: The study was carried out on adults aged 18 years and above. Study population consisted of four groups. Group-1 (control): healthy and history of no prior SARS-CoV-2 infection and vaccination, Group-2: had past SARS-CoV-2 infection and no vaccination, Group-3: received two doses of recombinant adenoviral vector vaccine ChAdOx1 (Oxford–AstraZeneca) without past SARS-CoV-2 infection, and Group-4: had past SARS-CoV-2 infection and received 2 doses of ChAdOx1 vaccination. Blood was collected 1 and 7 months after the second dose of vaccination from Group-3 and 4 individuals. Single blood sample was collected from participants of Gr-1 and 2 at the time of enrolment. Immunoglobulin G (IgG) antibodies to receptor-binding domain (RBD) of SARS-CoV-2 spike protein S1 (anti-RBDS1 IgG) was determined in serum by ELISA method. Results: Total 176 participants aged 18 years and above were enrolled. Anti-RBDS1 IgG positivity rates were 51.9%, 66.7%, 96.8% and 100% in individuals of Group-1, 2, 3 and 4 respectively. Gr-4 had significantly (p < 0.05) mean higher anti-RBDS1 IgG antibody level (120.8 ± 31.9 DU/ml) compared to other groups 1 month after 2nd dose of vaccination. No significant differences in antibody response were found among the individuals of four groups across gender and comorbidities. Seven months after the 2nd dose of vaccines, the antibody concentration declined in 85.3% (112.1 ± 30.4 DU/ml to 75.9 ± 48.7 DU/ml) and 81.5% (127.3 ± 20.4 DU/ml to 92.5 ± 43.6 DU/ml) individuals of Group-3 and Group-4 respectively. Decline of antibody was 40.6% and 34.7% in 7 months, but all remained positive except 1 in Group-3. Fever (34.4%) and headache (24.8%) were the most common adverse effects noted after vaccination. Conclusion: The study revealed that ChAdOx1 nCoV-19 vaccine induces high concentration of persisting anti-RBDS1 IgG antibody after 2nd dose and previous infection with SARS-CoV-2 acts as immune priming. Therefore, antibody screening test prior to booster dose could be a good option to maximize coverage of vaccination. IMC J Med Sci. 2023; 17(1): 009. DOI: https://doi.org/10.55010/imcjms.17.009 *Correspondence: J. Ashraful Haq, Department of Microbiology, Ibrahim Medical College, 1/A Ibrahim Sarani, Segunbagicha, Dhaka, Bangladesh. Email: jahaq54@yahoo.com