Evaluation of circadian rhythm of SARS-CoV-2 interferon-gamma release assay (IGRA) in healthy vaccinated individuals: a case-series

Background: The assessment of immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) includes both humoral and cellular immunity. The T-cell response plays a key role in reducing the risk of developing severe forms of coronavirus disease 2019 (COVID-19). Similar to other aspects of physiology and immune system, the adaptive immune system is regulated by circadian clocks. This study aimed to determine whether cellular immunity against SARS-CoV-2 may vary throughout different times of day after COVID-19 vaccination. Case Description: The study population consisted in four ostensibly healthy healthcare workers who received a single booster vaccination with the new bivalent BNT162b2 mRNA vaccine (Comirnaty, Pfizer/ Biontech, NY, USA) in November 2022. Blood samples were collected for three days at three different time points (9 am: T1; 2 pm: T2; 5 pm: T3). Cellular immunity was assessed using Roche Elecsys interferon-gamma (IFN-γ)-releasing assay (IGRA) SARS-CoV-2 at each time point, as IFN-γ response. The difference between the values of IFN-γ response after vaccination with BNT162b2 mRNA in the four subjects did not show a uniform and consistent trend. Even when adjusting the antigen-triggered value of interferon-γ for the value of the positive control, no uniform circadian trend appeared throughout the study period in the four subjects. Conclusions: In this four-case series, we found no evidence of circadian variation of cellular immunity assessed with IFN-γ response after BNT162b2 mRNA bivalent vaccination. Although the measurement of cellular response against SARS-CoV-2 with IGRAs does not seem to follow a clear trend influnced by circadian bias, the large interindividual variability suggests that the timing of sampling should be standardized when multiple assessments or interindividual comparisons are needed.