Depending on the overall magnitude and quality of the memory response and the incubation period of the pathogen, it can be eliminated prior to the establishment of the infection. Elimination of the pathogen even before it can infect a host cell and replicate, ideally directly at the site of entry, is referred to as sterilizing immunity (see Box 1 for glossary of terms). Antibodies are the main mediators of sterilizing immunity, but T cells may contribute to the elimination of infected host cells before the pathogen starts to replicate. By definition, sterilizing immunity prevents pathogen transmission.
The money shot:
Strong humoral responses in the upper respiratory tract might be necessary for protection from the infection at the site of virus entry, but potent mucosal immunity is not easy to achieve by vaccination.
A vaccine injected into the deltoid, that only stimulates a spike (S) protein response and not spike (S) + nucleocapsid (N) as would a natural infection, is not going to help there either.
A very accessible paper worth sharing.