Inoculation with an mRNA vaccine provides recognition of few antigena (e.g. RBD). The size of the vaccine dosage and the delay of a month between doses is designed to create a strong recognition of the chosen antigens.

Infection's response to key antigens like RBD is inherently more limited because: 1) immunity creates antibodies and T cells that target a wider range of antigens, and 2) exposure to COVID antigens usually fades after 7-10 days, limiting the immune system's time to build further defenses.