Upper respiratory tract mucosal immunity for SARS-CoV-2 vaccines.

SARS-CoV-2 vaccination significantly reduces morbidity and mortality, but has less impact on viral transmission rates, thus aiding viral evolution, and the longevity of vaccine-induced immunity rapidly declines. Immune responses in respiratory tract mucosal tissues are crucial for early control of infection, and can generate long-term antigen-specific protection with prompt recall responses. However, currently approved SARS-CoV-2 vaccines are not amenable to adequate respiratory mucosal delivery, particularly in the upper airways, which could account for the high vaccine breakthrough infection rates and limited duration of vaccine-mediated protection. In view of these drawbacks, we outline a strategy that has the potential to enhance both the efficacy and durability of existing SARS-CoV-2 vaccines, by inducing robust memory responses in the upper respiratory tract (URT) mucosa.