Viral vector vaccines: what are they, and how do they work?

We heard earlier how vaccines work in general, but there are differences between how they achieve their protective effects. AstraZeneca’s vaccine is what’s called a viral vector vaccine, and here’s Adam Murphy to explain how it works…

Adam - Vaccines rely on showing the immune system what a potential infection “looks” like. One way to do this is to “smuggle” the genetic message for making a few key parts of the infection into the body, and then to rely on our own cells decoding that message and making the pieces of the infecting organism themselves. When they do this, the pieces are presented to the immune system as though the infection were there, growing in the body for real, and this can produce a very powerful response. Of course, the infection isn’t really present so this is a very safe approach. The question is how to get that genetic message into the body in the first place. And it turns out that, because viruses themselves have naturally evolved to be very efficient at invading and hijacking our cells, they make excellent Trojan Horses - or vectors - for doing just this.

So scientists take a virus, and first disable it by removing its own genetic instructions that tell it how to grow. This means it’s harmless in the body. They then add the instructions for making - in the case of the coronavirus vaccine - the “spike protein” that the coronavirus uses to get into our cells when it infects us. This means that, when the disabled virus is injected into the body, it penetrates our cells, and although it can’t itself grow, it does cause the cells to temporarily churn out pieces of the outer coat of the coronavirus. These are presented to the immune system, and trigger it to produce a protective response.

AstraZeneca’s vaccine works this way, as does the Russian Sputnik V vaccine, and Janssen’s vaccine, which all use disabled cold viruses to carry the coronavirus spike message into the body. These vaccines tend to be very safe and very easy to store and transport. But one downside is that, because they use a virus to carry in the coronavirus message, the immune system will also react to the viral vector itself, potentially limiting the number of times they can be used in the same individual…