FIGURE 4.

Gradations of protective immunity. “Protection” can be defined many ways and can be categorized based on COVID‐19 disease severity. Sterilizing immunity can only be provided by antibodies at the portal of entry. Prevention of detectable infection (e.g., a positive test) can be accomplishing by neutralizing antibodies and possibly tissue‐resident T cells. Prevention of hospitalization‐level COVID‐19 or fatal COVID‐19 can likely be accomplished by multiple branches of adaptive immunity acting together over time