HOW THE JABS ARE MANUFACTURED

1. Grow a tank of bacteria that carry the gene for the target antigen

Scientists put a ring of DNA called a plasmid into bacterial cells. The plasmid carries the gene for the antigen. The bacteria then multiply and make many copies of the plasmid.

2. Burst open the bacterial cells

The cells are separated from the liquid in which they grew and then burst to release the plasmids. A series of purification steps follow, to yield a substance that will eventually contain only the plasmids.

3. Add enzymes into the mix

mRNA can only be made from a straight piece of DNA. But because the target gene sits in a closed ring of DNA, it needs to be snipped out. This is done by adding a particular enzyme into the mix. An enzyme is a molecule that helps cellular reactions along.

Another type of enzyme lets the two strings of DNA, which are twisted around each other, separate. And yet another enzyme then makes an mRNA molecule from one of the single DNA strings. This is called transcription.

4. Gather the mRNA molecules

The mRNA molecules are extracted from the solution by passing it through a thin tube filled with a solid material. The properties of this material make the mRNA molecules stick to it, after which the column is rinsed to get a solution that contains pure mRNA. This is now called the drug substance.

5. Wrap the mRNA in fat bubbles

The drug substance is mixed into a liquid that will cause it to become surrounded by small fat bubbles, called lipid nanoparticles. A few other ingredients, such as sugar, salts and fats, are also added to this mix to make up a concentrated form of the drug product — the stuff that goes into the shot to kick your immune system into gear to make antibodies.

6. Get ready to fill the vials

Only a very small amount of mRNA molecules is needed in a single jab. So the concentrated drug product has to be diluted a lot before it can be put into vials. The diluted form is called the final drug product.

7. Fill and cap the vials

In the case of Afrigen’s Covid-19 vaccine, each vial contains enough vaccine for 10 doses. Vials move along a small conveyor system and each one gets filled by a machine. Each one is sealed with an aluminium cap and then labelled.

About 30 different quality tests are performed during the production process to prove to a medicines regulator that the vaccine makes the grade. For example, the developer has to be able to show how well the vaccine keeps over time at different temperatures.