The basis of protective immunity from a successive infection is the immune memory derived from either primary infection or immunisation.30,31,32 Recently, a predominantly cross-sectional study, which also included a longitudinal component of 188 recovered COVID-19 cases, assessed the involvement of the CD4+ T-cell, CD8+ T-cell, and humoral components of adaptive immunity in the immune memory. The gene discussed is CD4; the disease is infection.