Study of the cellular and humoral immune responses to SARS-CoV-2 vaccination

Our understanding of cellular immunity in response to COVID-19 infection or vaccination is limited because of less commonly used techniques. We investigated both the cellular and humoral immune responses before and after the administration of a third dose of the SARS-CoV-2 vaccine among a group of healthcare workers. Cellular immunity was evaluated using the VIDAS interferon-gamma (IFN gamma) RUO test, which enables automated measurement of IFN gamma levels after stimulating peripheral blood lymphocytes. Booster doses significantly enhanced both cellular and humoral immunity. Concerning cellular response, the booster dose increased the percentage of positive IFN gamma release assay (IGRA) results but no difference in IFN gamma release was found. The cellular response was not associated with protection against SARS-CoV-2 infection. Interestingly, vaccinated and infected healthcare workers exhibited the highest levels of anti-spike and neutralizing antibodies. In conclusion, the IGRA is a simple method for measuring cellular immune responses after vaccination. However, its usefulness as a complement to the study of humoral responses is yet to be demonstrated in future research.