Viral vector vaccines use harmless viruses to deliver genetic material from a pathogen, like the SARS-CoV-2 virus that causes COVID-19. This genetic material instructs cells in the body to produce a harmless piece of the pathogen, prompting an immune response without causing disease. Once the immune system recognizes this piece as foreign, it generates antibodies and trains immune cells to fight the actual pathogen if encountered in the future. This method is effective because it mimics a natural infection, helping the body prepare for real threats while remaining safe.