Vol. 5, Issue 2, Part A (2023)

Background: COVID-19 immunity can be acquired by vaccination or by natural infection with SARS-CoV-2. The choice of immunisation method depends on a country's resources, the risks involved and the availability of vaccines during the period of high endemicity. Many public health authorities have opted for vaccination protocols that give priority to people at high risk. People who had already been infected may not have been given priority because of existing humoral immunity. 
Objective: We compared residual antibody levels between previous COVID-19 infection and COVID-19 vaccination in medical staff. 
Methods: A serological assay using a competitive enzyme-linked immunosorbent assay for the quantitative determination of total neutralising anti-S1 SARS-CoV-2, IgG and IgM antibodies on a disposable device with the Chorus TRIO was performed on healthcare staff from the three university teaching hospitals in Abidjan-Côte d'Ivoire. Our population was categorised into 2 and then 4 groups, and antibody levels were compared between the different groups using the Kruskal-Wallis test. 
Results: A total of 275 people were recruited with a mean age of 40.1 years. Within each type of immunisation, there was a significant difference between the medians of IgG and neutralising antibodies of vaccinated subjects compared with non-vaccinated. However, among those with a history of infection, there was a difference only in IgG. Neutralising antibody levels were comparable to subjects with no previous infection. IgG and neutralising antibody levels were higher in people with hybrid immunity compared with those with only one mode of immunisation. Hybrid immunity was comparable to immunity acquired by infection in terms of IgG and comparable to vaccination in terms of neutralising antibodies. 
Conclusion: Vaccination appears to result in better production of neutralising antibodies, whereas infection results in better production of IgG. Protection against COVID-19 appears to be better with hybrid immunity.