day 0 and 28 and sacrificed for serum antibody measurements or challenged with live virus on day 56. On day 58, challenged mice were sacrificed and lungs obtained for virus and histopathology.
The test vaccines didn't kill them, the mice were killed in order to study lung tissue and serums. This is relatively standard practice.
Did you actually read the literature?
day 0 and 28 and sacrificed for serum antibody measurements or challenged with live virus on day 56. On day 58, challenged mice were sacrificed and lungs obtained for virus and histopathology.
The test vaccines didn't kill them, the mice were killed in order to study lung tissue and serums. This is relatively standard practice.