Intranasal vaccination produces potent systemic immunity against HIV and SARS-CoV-2 in animal models

Even though most viruses cause infection directly through mucosal cells, the vast majority of vaccines are administered intramuscularly in a cellular mismatch that doesn't always produce optimum immunity.

source https://medicalxpress.com/news/2022-08-intranasal-vaccination-potent-immunity-hiv.html