Why doesn't vaccines come prefilled in syringes?

I fail to understand why someone would decide that Hacker News is the appropriate site to ask this kind of question.

That would be coupling a syringe and a substance. You want to have them as separate inventory items.

There's also the lyophilization[0] aspect, or water removal by sublimation, to dramatically increase the shelf life of the substances. It is a thing of beauty.

[0]: https://en.wikipedia.org/wiki/Freeze-drying

They need to be refrigerated. Vials take up a lot less space in a fridge.

Beyond the valid supply chain issues, there's also the problem of having to prevent the plunger from being depressed and leaking vaccine.

The point of the plunger is that, when pressed, it pushes the vaccine out the tip of the needle. When needles are shipped empty, they can be thrown in a bag with other needles, and the box doesn't need especially careful handling. The plunger can be shipped completely depressed, and the needle being rattled around won't move the plunger. And even if the plunger does move, it's not a problem.

But what if the needle has vaccine in it? Then the needle ships with the plunger raised. The needle will have to have hardware to prevent the needle from depressing while in transit. Needles are capped, yes, but the current cap does not have to be waterproof; it's just a cover to make the needle safer.

And what if the needle does get slightly depressed, and we lose some vaccine? Even if we had vaccine in a bottle, it's a bad idea to mix vaccine lots! So we have to throw out the needle and vaccine entirely.

I am not all qualified to answer this but I will guess. I would assume "separation of duties". A Syringe's job is to be available to administer any vaccine at the time of delivery. If you prefill a syringe, you now have to ensure it is only used for that vaccine purpose and then you also have to label it properly. More work. Vaccine package anyway needs to be properly labeled but now you are introducing another overhead to track/manage/label the syringes.

Logically, it makes sense to keep the 2 separate. This way, you can use any good syringe when needed while ensuring there is no confusion on which vaccine was administered.

Also, this ensures that you don't need a 1-1 relationship between syringe and vaccines. Lets say you produced a million vaccines. There is no need to produce a million syringes at the same time. You can just ship the vaccine to whichever clinic/hospital/authority and they can decide how to distribute and get syringes at the time.

How is this for a guess ?

Why do you think it would be fewer steps, or less waste? The syringes would need to be shipped first from the syringe manufacturer to the vaccine manufacturer, unpackaged, integrated into the manufacturing process there, then repackaged and reshipped to the vaccinators. Meanwhile the vaccinators already purchase syringes for their ordinary medical practice.

Furthermore, vaccines need to be refrigerated while syringes do not. If you combine them too early in the process, then the whole syringe ends up needing to be refrigerated. This increases the mass and volume that needs to be refrigerated, complicating the entire logistical network for distributing the vaccine.

Many medicines and some vaccines are given in varying doses based on the weight of the patient; as well as there being many reasons that one might need to use a different syringe or needle on a particular case than the standard kit has...

They sell pet vaccines in single dose kits; those come with a syringe and 2 vials, usually, and you use the syringe to put saline (I assume, some liquid) on the dried vaccine agent then reload it. I don't recall seeing a single vial or pre-loaded syringe.

I assume that's because plastic syringes aren't great packaging. The rubber topped glass vial protects from air better than plastics will.

Syringes would be easier to adulterate, are made of plastic (could have substances that modify or mess with the vaccine compounds, glass is inert and clean) and would add several extra problems in the manufacturing part like leakage, disassembling when filled or breaking.

Following the same reasoning an even better way to do it would be a big bottle connected with a machine that would deliver the correct dose. Such machine should fulfill at least the next points

1) Assure the vaccine integrity and identify. Grant that the product has not been modified at any point (closed metallic bottle that can't be pierced or manipulated with an official seal difficult to duplicate or fake.

2) Keep the product refrigerated and watch its temperature all the time.

3) Travel. A metallic bottle would stand transport much better than glass and would need less packaging materials.

Autonomous system can be just put in a pickup and moved to places without accurate refrigeration. Not need to build expensive rooms or hospitals and reaching isolated areas

4) Assure the same dose to everybody and change automatically the needle without the need of any human hand near the needle's boxes. Avoiding injuries and diseases

5) Discard safely the used needle and trow it into a secure recycling compartment.

6) Allow people to enter their own personal data and ID card in a keyboard or card slot before being vaccinated. then, keep this data safe stored into a database far from curious eyes

7) Share the number of vaccines used in real time or almost with the other teams. Thus the government could know what machines must be refilled and how many old needles boxes should be replaced in real time and plan according. If a place is not getting enough stream of people, the machine could be recalled to the next near place that is too busy

8) Avoid the human factor. Machines are tireless and fast. Don't need to make breaks or sleep as humans, don't care about skin color and can be bribed by local corrupts or the hate department.

Automatic vaccining machines could made a bigger difference than vaccines prepackaged in syringes, for sure, I wonder why nobody has created one still.

Syringes are generic (and cheap). Pre-loading them would greatly complicate the shipping, tracking and storage of the vaccine. I'm sure there are other reasons, but those comes to mind most readily.