I've been looking at how the Astrazeneca Covid-19 vaccine works:
A chimpanzee adenovirus (the viral vector) is injected into the patient. After entering a cell, the viral DNA is deposited in the host cell nucleus.
- The viral DNA only contains information about the SARS-CoV-2 spike protein.
- The viral DNA does not integrate with the host cell DNA.
mRNA is transcribed from the viral DNA, and this mRNA is translated into the SARS-CoV-2 spike protein. This is displayed on the surface of the cell where it is recognised as an intruder by the immune system which then begins producing antibodies.
Pre-existing immunity is recognised as a potential problem. From Medical News Today - COVID-19: How do viral vector vaccines work?:
With all viral vectors, one issue to consider is pre-existing immunity. If a person encountered the virus that serves as the vector in the past, they may have antibodies to the virus. This means that their body will try to fight and destroy the viral vector, potentially making a vaccine less effective.
But where is the innate immune system in all this? My (layman's) understanding is that the very fact that the virus particle was novel would result in an immediate response from the innate immune system. How does the viral vector get past it?