CD4 and infection: Interferon-γ expression by CD4+ T-cell induction also tends to reduce in severe cases compared to moderate cases.4 It takes between 10 and 21 days after infection for antibody response to develop in most SARS-CoV-2-infected persons, and it takes between 6 and 15 days after the onset of disease for the immunoglobin M and immunoglobin G antibodies to SARS-CoV-2 to develop.25,26,27,28,29 In mild cases, antibody development can take up to 4 weeks or longer and may even be undetectable in a small number of cases.