Background and objectives: COVID-19 vaccination program has become a global priority to combat the worldwide pandemic. Studies claimed that severity and case fatality could be minimized by vaccination. The durability of antibodies developed after vaccination is crucial for preventing COVID-19. The purpose of this study was to investigate the dynamics of antibody responses to an inactivated SARS-CoV-2 virus vaccine over time.

Materials and method: The study was conducted from November 2021 to November 2022 among young adults. A pre-tested structured questionnaire was used to record the socio-demographic and clinical data of all the participants. All the participants were vaccinated with two doses of Sinopharm COVID-19 vaccine. Blood samples were collected for estimation of IgG antibodies to SARS-CoV-2 spike S1 protein by indirect ELISA. Biochemical parameters namely random blood sugar (RBS), lipid profile, total protein, thyroid stimulating hormone (TSH), FT4 (free thyroxin) and vitamin D levels were determined in baseline samples by standard methods.

Result: Total 348 adults, aged 18-28 years, were enrolled and of which 35.3% and 64.7% were male and female respectively. Out of 348 participants, 51.7% was seropositive for anti- SARS-CoV-2 antibodies before receiving vaccination. Seropositivity was not significantly (p >0.05) different in male and female participants before and after vaccination. Seropositivity at 1 month after 1^st dose and 4 and 7 months after 2^nd dose of vaccination increased significantly (p <0.05) compared to pre-vaccination rate. Compared to pre-vaccination level, the mean anti- SARS-CoV-2 antibody levels increased significantly (p<0.05) at 1 month after 1^st dose and 4 and 7 months following 2^nd dose of vaccination. Among 41 seronegative (non-immune) individuals, seropositivity to SARS-CoV-2 increased significantly (<0.05) at 7 month after 2^nd dose of vaccine compared to 1 month and 4 months following 1^st and 2^nd doses of vaccine respectively. Seropositivity was not significantly (p >0.05) different before and after vaccination in participants having adequate and insufficient/deficient vitamin D levels.

Conclusion: The study revealed that a good proportion of young adults possessed anti- SARS-CoV-2 antibody before vaccination and the seropositivity increased to over 90% following vaccination with Sinopharm COVID-19 vaccine. High level of anti- SARS-CoV-2 antibody persisted 7 months after 2^nd dose of vaccine.

July 2024; Vol. 18(2):012.  DOI:https://doi.org/10.55010/imcjms.18.024

*Correspondence: Nehlin Tomalika, Department of Community Medicine & Public Health, Ibrahim Medical College, 1/A, Ibrahim Sarani, Segunbagicha, Dhaka 1000, Bangladesh. Email: [email protected]