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 plun

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.