Immunological markers induced by infection, such as nasal mucosal S-specific secretory IgA antibodies21, which are also associated with a reduction in the duration of virus shedding after infection22 and blood circulating N-specific CD4+ and CD8+ T cells induced by infection, but not spike-based current vaccination, associated with the prevention of infection, have been reported to negatively correlate with peak upper respiratory tract viral loads38. Here, CD4 is linked to infection.