Figure 4.

CD8⁺ T cell responses decay after SARS-CoV-2 infection but vaccination boosts memory against spike protein. CD8⁺ T cell responses were measured longitudinally by ELISpot assay in 29 persons monitored starting early SARS-CoV-2 infection (23 with mild infection, 6 with severe infection, starting <45 days after symptom onset), serial measurements are plotted for 23 total spike responses (A), 24 total nucleocapsid responses (B), and 16 total matrix responses (C). (D) For 17 persons with prior COVID-19 who were vaccinated with an available pre-vaccination measurement within 65 days (14 with mild infection, 3 with severe infection including one who had critical infection, vaccinated mean of 225 days post onset of symptoms, range 64 to 394 days), baseline pre-vaccination (mean of -21.9 days, range -63 to +3 days before vaccination) and resulting post-vaccination (first dose, mean of 12.8 days, range 5 to 29 days after vaccination) total response levels against spike and combined nucleocapsid plus matrix are plotted. Eight vaccinees received BNT162b2 (red), seven vaccinees received mRNA-1273 (blue), and two vaccinees received Ad26.COV2.S (green). Two non-responders had no detectable response at baseline and received BNT162b2. One non-responder had prior severe illness and the remainder had mild illness. (E) For the vaccinated persons, Sørenson similarity values were calculated between pre- and post- vaccination recognized spike pools within each person (self) and across all combinations with other persons (others). Box plots indicate 25th to 75th quartiles and medians, with medians (horizontal line) and means (x) marked. The high background similarity between individuals resulted from the high number of unrecognized pools (average 10.2/12 pools) and thus multiple shared unrecognized pools across persons.