By health reporter Olivia WillisPosted Wed 18 Aug 2021 at 5:00amWednesday 18 Aug 2021 at 5:00am, updated Wed 18 Aug 2021 at 10:13am
How do vaccines mimic a virus?
In order to train our bodies to recognise pathogens (and fight them off down the track), vaccines introduce our immune system to part of a pathogen — known as an “antigen” — which triggers an immune response.
This antigen might be a weakened or inactivated virus, or it might be just one part of a pathogen — for example, the spike protein found on the surface of SARS-CoV-2 (used by the virus to latch onto and enter human cells).
Traditional vaccines, including some COVID-19 jabs, deliver antigens directly to the body.
But other COVID-19 vaccines, such as the Pfizer, Moderna and AstraZeneca jabs, use different technology.
Instead of delivering the antigen itself, the vaccines contain a genetic blueprint (or set of instructions) that tell the body to make the SARS-CoV-2 spike protein using the body’s own cells.
To do this, the Pfizer and Moderna jabs contain a single strand of genetic material — that’s the mRNA or messenger RNA — which is encapsulated in a protective fatty coating.
The AstraZeneca vaccine, on the other hand, contains double-stranded DNA, which is carried into the body via a weakened version of a common cold virus, engineered so it doesn’t replicate.
“The DNA gets taken up by your cells, that DNA then encodes the mRNA, and then it turns into a protein … which is what your body is going to respond to,” says Stuart Tangye, an immunologist from the Garvan Institute of Medical Research.
“The mRNA vaccine just skips that first step.”