What are viral vector-based vaccines and how could they be used against COVID-19?

How do such vaccines trigger immunity?

Once injected into the body, these vaccine viruses begin infecting our cells and inserting their genetic material-including the antigen gene-into the cells’ nuclei. Human cells manufacture the antigen as if it were one of their own proteins and this is presented on their surface alongside many other proteins. When the immune cells detect the foreign antigen, they mount an immune response against it.