Consistent with ELISpot data, we detected a significant increase in the frequencies of IFN-γ producing CD4+ T cells upon stimulation with either P1 or P2 mRNAs compared with mock stimulation regardless of participants' past infection status (0.09% and 0.09% for P1 mRNA and P2 mRNA, respectively vs 0.05% for mock, p < 0.001, Figure 4D & Supplementary Figure 6A). Here, CD4 is linked to infection.