PROS1 and infection: In order to more comprehensively evaluate the immune responses after vaccination, we analyzed the S protein-specific T-cell response (IFNγ-secreting cells) with the enzyme-linked immunospot assay (ELISPOT) at 0, 2, and 6 weeks after the volunteers were vaccinated.26,33–36 It was shown that the proportion of S protein-specific T cells in the prior infection group increased rapidly after the first injection, and both the naive and prior infection group could induce good T-cell responses after two doses (supplementary Fig. 5).