At the back of a building in Melbourne's northern outskirts is a long, narrow room roughly the area of a tennis court.
Technicians and operators — fully decked out in protective onesies, gloves, goggles, hairnets and masks — bustle about, tending to a vast array of gleaming stainless steel equipment and what looks like kilometres of plastic tubing.
There are people here at all hours, too — it's a 24/7 operation.
That's because this room, part of CSL's Broadmeadows plant, is where 50 million doses of the Oxford-AstraZeneca COVID-19 vaccine will be grown.
Earlier this week, the vaccine was approved by the Office of the Gene Technology Regulator. It's currently under review at the Therapeutics Good Administration.
And when millions of Australians roll up their sleeve to get the vaccine, the shot itself may only take a couple of seconds, but it will have been three months in the making.
How the AstraZeneca vaccine works
- The AstraZeneca COVID-19 vaccine is a viral vector vaccine
- It enlists the help of a harmless virus, in this case a chimpanzee adenovirus ChAdOx1, to deliver a payload of genetic material into our cells
- The genetic material is in a ring of DNA and contains a blueprint to make the spike protein on the virus that causes COVID-19, SARS-CoV-2
- When it's injected into our arm, the adenovirus slips the DNA ring into our cells
- Our cells "read" the DNA instructions and make spike proteins, then push them outside the cell to trigger an immune response
- After a time, the DNA ring is broken down and disposed of by our cells' waste management system
Hosts with the most
The AstraZeneca vaccine is what's known as a biological. It needs the help of living organisms to be produced.
Loads of pharmaceuticals are produced this way, including vaccines. The HPV vaccine, for instance, which protects against cervical cancer, is one.
The AstraZeneca COVID-19 vaccine relies on a type of cell called HEK 293. These cells were originally taken from a human embryo kidney — hence HEK — back in the 1970s. They grow well in labs and are a commonly used component in drug manufacturing.
HEK cells don't actually end up in the vaccine. Instead, they cultivate the crucial part of the vaccine — the adenovirus, which carries the spike protein DNA blueprint.
So the first step in making the AstraZeneca vaccine is to grow an army of HEK cells.
Just as you might get sourdough starter from a friend, AstraZeneca, in November, supplied CSL with tiny frozen tubes, each holding a mere millilitre of HEK cells.
CSL's job was to take these smidgens and get them multiplying to fill the equivalent of a small water tank.
And it's not a simple matter of popping the cells in a massive tub, adding a broth of nutrients and other substances, and letting them grow.
HEK cells prefer company. They multiply faster if they're crowded with others.
So the cells start in a 10ml glass flask. Once they've filled that, they're transferred to a slightly larger one, maybe 50ml, and so on. (It's a little like a hermit crab outgrowing its shell and finding a bigger one to move into.)
Eventually, the cells are relocated into plastic sacks, like bigger versions of blood donor bags, and are gently swayed on moving platforms. The swirling motion helps them grow.
And eventually, the now-many-litres of HEK cells are poured into the bioreactor: a 2,000-litre stainless steel vat standing more than 3 metres tall.
After a few days, the HEK cells, happily living and multiplying away in the bioreactor, are ready for the next step.
Introducing the adenovirus
At this point, around three weeks in, the adenovirus comes into the vaccine-making process — literally.
Also supplied in tiny tubes by AstraZeneca last November, the adenovirus is added to the bioreactor and the waiting HEK cells.
And while the adenovirus is engineered so it can't replicate in human cells — it's missing the essential genes that allow it to happen — the HEK cells have been tweaked to encourage the adenovirus to infect and replicate in them.
Over the next six days, the adenovirus infects the HEK cells, multiplies, and goes on to infect more HEK cells.
The infected HEK cells inevitably die. But in their wake, the amount of adenovirus dramatically increases.
Next, it's time to filter and purify the adenovirus from the pale pink bioreactor broth.
This is done using a technique called capture chromatography.
The liquid trickles through membranes that are designed so the adenovirus sticks to them, but everything else flows right on through.
A different liquid is then sent through the membranes, changing their charge so they relinquish their hold on the adenovirus, which is then collected.
The bulk concentrated adenovirus vaccine is frozen at -65 degrees Celsius in 20-litre plastic "cryovault" containers.
And their job now done, any remaining HEK cells are destroyed.
Fill and finish (and testing)
That first part — the growing, harvesting and freezing — takes place over about six weeks at CSL's Broadmeadows site.
The next six weeks involves diluting the vaccine to the correct concentration, packaging it up, tonnes of testing and getting it ready to be sent to clinics for use. This is dubbed "fill and finish" and will be done at the Parkville facility, 14km south of Broadmeadows, starting next week.
And while it sounds straightforward, it's easier said than done.
The adenovirus vaccine can only last so long when it's not refrigerated. So from the moment the vaccine ice blocks are removed from their deep freeze, the clock is ticking.
First, cryovault blocks are thawed — again, on a rocking platform — at room temperature. This takes more than a day.
The liquid concentrate is then mixed with a buffer solution to make up around 200 litres, tested for its concentration (which takes a few hours) and then adjusted to the level set out by AstraZeneca.
Why not inject the straight adenovirus? The buffer solution does a few things, such as stabilising the vaccine and maintaining its pH.
Once the vaccine is mixed, it's passed through two pharmaceutical filters to ensure it's completely free of any bacteria or other viruses.
The sterile liquid is finally shuttled to the filling section, where 6.5ml — that's 10 doses — are squirted into sterile glass vials and capped with a layer of aluminium and a rubber stopper.
(The air above the vaccine is classified as "Grade A" air — the cleanest pharmaceutical grade air as determined by global regulations.)
It takes around 12 hours to put 200 litres into those vials, and each batch ends up providing around 300,000 doses.
But that's not the end of the process — not by a long shot.
Then there's nearly a fortnight of inspections and at least 14 tests — not including those conducted by the Therapeutic Goods Administration at its Canberra labs — and a final documentation check by AstraZeneca.
AstraZeneca, ultimately, gives the final green light to release the vaccine.
And then, after 12 weeks, it's ready to use.
Safety and specifications
The whole vaccine process is done according to stringent specifications laid out by AstraZeneca.
Batches are tested at all stages, from the raw materials, like the chemicals used to grow HEK cells and the bags they live in, as well as for contamination and purity.
Even the quality control testers, who inspect each vial after its filled, undergo rigorous training beforehand. They're given an array of vials to inspect. Some have hidden defects.
They must find all the defects three times to get qualified.
And not all vials are expected to make it past the post. Between 2 and 5 per cent will probably be rejected, based on previous vaccine manufacturing processes.
Despite getting the production line up and running in a few months — a process that would normally take the best part of a year and a half — it's still early days for CSL. The first couple of batches didn't yield as much adenovirus as expected.
But that's the nature of using living organisms, like HEK cells, to make something. You just don't know how they're going to act each time.
In any case, the production line at Broadmeadows continues. Multiple batches at various stages in the pipeline keeps the product pushing through.
And once the first batch of the vaccine is released, the company hopes to have north of a million doses coming off the line each week — with the potential to double that down the track.
Source: ABC Science
