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 2^nd 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 2^nd 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 2^nd 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: [email protected]