What Proportion of Population has achieved Cellular Immunity against SARS-CoV-2 after Booster Vaccination: A Cross-sectional Study

Abstract

Background Booster vaccination reduces the incidence of severe cases and mortality of COVID-19, with cellular immunity playing an important role. However, little is known about what proportion of population has achieved cellular immunity after booster vaccination. Methods We conducted a Fukushima cohort database and assessed the humoral and cellular immunity in 2526 residents and HCWs in Fukushima Prefecture in Japan by continuous blood collection every 3 months since September 2021. We identified the proportion of people with induced cellular immunity after booster vaccination, using T-SPOT.COVID test, and analyzed their background characteristics. Results Among 1089 participants, 64.3 % (700/1089) had reactive cellular immunity after booster vaccination. Multivariable analysis revealed the following as independent predictors of reactive cellular immunity: age <40 years (adjusted odds ratio: 1.81, 95 % confidence interval: 1.19–2.75, p-value: 0.005), and adverse reactions after vaccination (1.92, 1.19-3.09, 0.007). Notably, despite IgG(S) and neutralizing antibody titers of ≥500 AU/mL, 33.9 % (349/1031) and 33.5 % (341/1017) of participants, respectively, did not have reactive cellular immunity. Conclusion This is the first study to evaluate cellular immunity at the population level after booster vaccination using T-SPOT.COVID test, however, with several limitations. Future studies will need to evaluate previously infected subjects and their T-cell subsets.