FIGURE 3.

Mucosal and systemic antiviral responses after SARS‐CoV‐2 infection and vaccination. Mucosal exposure to viral antigen (by natural infection or by intranasal immunization) leads to in situ as well as systemic activation of virus‐specific adaptive immune cells. With intramuscular immunization, mucosal exposure to antigen is not present, therefore, only generating systemic but not mucosal immune responses. With mucosal antigen exposure, there is generation of tissue‐resident memory lymphocytes and ASC that locally prevent infection upon subsequent virus exposures. Without mucosal responses but in the presence of systemic antiviral responses, there is protection against severe disease but less so against the early infection at the mucosal entry site. Ab, antibody; BTI, breakthrough infection