What this class of vaccine does is make a bunch of foreign proteins for your immune system to attack in your arm without actually infecting you with the disease. So you get inflammation and soreness at the injection site, and this is not from the physics of having an injection. The placebo arm injects with a saline solution, so there's no immune response, and you miss those symptoms.

From what I've heard from one of the trials, they used a meningitis vaccine that actually does hurt. (Its side effects are known but minor.)

That was hearsay, though, and I don't have access to the internal protocol.

The AstraZeneca trial was the one to use the meningitis vaccine.

No, the trial procedure is publicly available. They used a saline solution as the placebo.

I should have double checked on clinicaltrials.gov first. (I was thinking of the AstraZeneca trial.)

Do you think people could perceive having "false" inflammation? I'm thinking that if during the double blind trial they told those not getting the real dose that they should expect inflammation that many of them would believe they're having some form of inflammation.

Yes, it's called nocebo effect and can be quite harmful actually.

It might have been the trial for a different vaccine; I think it was the one someone on this site was participating in? But in that trial, the control was another proven vaccine for something most people don't commonly get vaccinated for.

I got muscle aches, fatigue, and headaches, but my arm never felt more than a little hot. I still have no idea which branch I'm in.

you probably got the vaccine, saline injections don't do that

That's what I thought, but my effects were mild compared to what I've heard other people reporting. Either I got milder side-effects because I'm young, or I'm fooling myself.

Many people get placebo effects