Viral vector vaccines are ineffective if the host has had previous immunity to the vehicle virus. True or false

Answer

True.

Viral vector vaccines utilize a modified virus (the vector) to deliver genetic material into cells, prompting an immune response. If the host had previous exposure to the vector virus, their immune system may recognize and mount a response against it rather than the intended target (the pathogen the vaccine is designed to protect against). This pre-existing immunity can neutralize the vector before it effectively delivers its payload, leading to inferior or null immunogenicity and rendering the vaccine ineffective.

Moreover, if the host has strong immunity against the vector virus, vaccination may lead to a rapid immune response that prevents the vector from replicating and delivering the necessary genetic material to induce a protective immune response against the intended pathogen. Therefore, the effectiveness of viral vector vaccines can be significantly hampered by prior immunity to the vehicle virus.