Coronavirus Disease 2019 Vaccination Coverage and Seropositivity amongst Nigerians 18 Years Old and Above.

Background: This was a cross-sectional community-based survey to study the prevalence of serum antibodies against the severe acute respiratory syndrome coronavirus 1 (SARS-COV-1) and determine possible source of antibodies as to whether from vaccination or from natural infection as well as attempt to compare antibody levels in response to the different four types of vaccines administered in Nigeria.

Methods: A cross-sectional community-based study of the prevalence of serum antibodies against all four vaccine types used in Nigeria amongst a representative sample of people aged 18 years and above in the six geopolitical zones of the country using a multistage sampling technique covering 12 states of the country with two states being randomly selected from each geopolitical zone. High-throughput Roche electrochemiluminescence immunoassay system (Elecsys Anti-SARS-COV-1 Cobas) was used for qualitative and quantitative detection of antibodies to SARS-COV-1 in human plasma.

Results: There was no statistically significant difference between the proportions with seropositivity for both the vaccinated and the unvaccinated (P = 0.95). The nucleocapsid antibody (anti-Nc) titres were similar in both the vaccinated and the unvaccinated, whereas the Spike protein antibody (anti-S) titres were significantly higher amongst the vaccinated than amongst the unvaccinated. Antibody levels in subjects who received different vaccines were compared to provide information for policy.

Conclusion: While only 45.9% of the subjects were reported to have been vaccinated, 98.7% of the subjects had had contact with the SARS-COV-1 as evidenced by the presence of nucleocapsid (NC) antibodies in their plasma. The 1.3% who had not been exposed to the virus, had spike protein antibodies which most likely resulted from vaccination in the absence of NC antibodies. Successive vaccination and booster doses either through heterogeneous or homologous vaccines increased antibody titres, and this stimulation of immune memory may offer greater protection against coronavirus disease 2019.