Evaluation of T cell responses with the QuantiFERON SARS-CoV-2 assay in individuals with 3 doses of BNT162b2 vaccine, SARS-CoV-2 infection, or hybrid immunity

Cellular immunity after SARS-CoV-2 infection or immunization may be important for long-lasting protection against severe COVID-19 disease. We investigated cellular immune responses after SARS-CoV-2 infection and/or vaccination with an interferon -g release assay (QuantiFERON, QFN), in parallel, with humoral immu-nity assessment. We recruited 41 participants: unvaccinated convalescent children and adults and vacci-nated uninfected or vaccinated convalescent adults. All vaccinated adults had received three doses of the BNT162b2 COVID-19 vaccine at 6.2 to 10.9 months prior to their inclusion to the study. All the unvaccinated participants were tested negative with QFN. Regarding the vaccinated population, 50% (8/16) of the vacci-nated uninfected adults and 57.1% (8/14) of the vaccinated convalescent adults were tested positive. QFN did not detect T cell responses in unvaccinated individuals and in a significant number of vaccinated individuals. Further comparative studies with different immunoassays are required to elucidate whether this is the result of waning immunity or low sensitivity of the assay.(c) 2023 Elsevier Inc. All rights reserved.

Automated summary

Cellular immunity may play a crucial role in providing long-term protection against severe COVID-19 disease after SARS-CoV-2 infection or vaccination. This study investigated cellular immune responses using the QuantiFERON assay, along with assessment of humoral immunity, in individuals who were either unvaccinated convalescents or vaccinated individuals. The results showed that a significant proportion of vaccinated individuals had detectable T cell responses, while unvaccinated individuals did not. Further studies are needed to determine whether this is due to waning immunity or the assay's sensitivity.