CD4 and COVID-19: Studies conducted prior to the global COVID-19 vaccine rollout demonstrated infection to drive significant expansion of spike-specific nAb, CD4+ and CD8 + T-cell responses42 and to be noticeably of greater magnitude than responses induced in seronegative unexposed subjects by CS or CO16 or indeed mRNA vaccines41 indicating primary immune responses induced by vaccination to be inherently of lower magnitude than that induced by infection.