Immunity to SARS-CoV-2 after vaccination and previous infection: COVID - 19 immunity study, Namibia

Background: Severe Acute Respiratory Syndrome Coronavirus Disease 2019 (COVID - 19) caused by SARS-CoV-2 virus has had a devastating global impact, leading to millions of deaths. The rollout of COVID - 19 vaccines has been critical in controlling the pandemic. In Namibia, the COVID - 19 vaccine rollout began in March 2021, with a national target of vaccinating at least 60% of the population. This study aimed to evaluate the immune response to COVID - 19 infection and vaccination with either Sinopharm, Covishield, Pfizer and Jansen vaccines. The study population consisted of participants residing in Oranjemund, Namibia. Methods and Results: We enrolled 260 participants, among which 80.4% had received COVID - 19 vaccination. Serum samples were collected between December 15, 2021, and June 15, 2022. Levels of anti-SARS-CoV-2 spike (anti-S) and anti-SARS-CoV-2 nucleocapsid (anti-N) antibodies in vaccinated and unvaccinated individuals were measured using qualitative and quantitative chemiluminescence immunoassays.  The results showed that 92.5%(n=112)  participants with laboratory-confirmed COVID - 19 infection had detectable anti-N antibodies, indicating immunity due to prior infection.  54.6% (n=76) of individuals without a history of infection also had reactive anti-N antibodies, suggesting immunity. All vaccinated participants showed the production of anti-S antibodies. 99.5% (n=187)  of individuals with anti-N antibodies had detectable anti-S antibodies. Notably, 7.5% (n=9) of participants with a history of COVID - 19 infection did not have detectable anti-N antibodies.  We found a strong correlation r 2 = 0.69 (p-value = 3.755e-11) between COVID - 19 diagnosis and testing positive (reactive) for Anti-N antibodies . Conclusions:  We found a high level of detectable anti-N antibodies in patients who had a history of COVID - 19 infection and anti-S antibodies in those who were vaccinated. The study provides insights into the immune response to COVID - 19 infection and vaccination in Namibia, contributing to the understanding of vaccine effectiveness and development of immunity.