Results SARC-CoV2-naive vaccinees had a 13.06-fold (95% Cl, 8.08 to 21.11) increased risk for breakthrough infection with the delta variant compare to those previously infected.
It is important to note that natural infection induces both mucosal antibody responses (secretory immunoglobulin A (lgA)) and systemic antibody responses (lgG). The upper respiratory tract is thought to be mainly protected by secretory lgA, whereas the lower respiratory tract is thought to be mainly protected by lgG. Vaccines that are administered intramuscularly or intradermally induce mainly lgG, and no secretory lgA. It is therefore possible that most vaccine currently in development induce disease-preventing or disease-attenuating immunity, but not necessarily sterilizing immunity.