How do vector vaccines work?

Vector vaccine
Image: Anne Seeger, SCNAT (CC BY 4.0)

Vector vaccines deliver the construction plan for a part of the virus. Produced in a laboratory, this construction plan consists of DNA. For the COVID-19 vaccine, the construction plan carries the instructions to produce the spike protein of the coronavirus. This protein covers the surface of the virus like spikes and is therefore easily recognisable by our immune system. In the case of the vector vaccine, the DNA is inserted into inactivated (and therefore harmless) adenoviruses so that the instructions can gain entry to the cells of our body.

After the vaccine has been injected into the muscle, the adenoviruses enter our cells and transport the DNA instructions to the cell nucleus, where proteins transcribe the DNA into mRNA. The mRNA then serves as a template for the ribosomes outside the cell nucleus to produce the spike proteins. The spike proteins are subsequentially transported to the cell surface where they can be detected as intruders by our immune cells. This activates the immune system and antibodies against the spike protein are produced. Moreover, an immunological memory is created in the form of memory B cells that offer protection against later infection.

Both vector vaccines and mRNA vaccines work by delivering to our cells the construction plans to produce the spike protein of the coronavirus. They differ when it comes to the type of the construction plan (DNA in the case of vector vaccines and mRNA in the case of mRNA vaccines) and their vehicles of delivery (adenoviruses in the case of vector vaccines and lipid nanoparticles in the case of mRNA vaccines).

Swissmedic has released a video explaining how vector vaccines work.