pla·ce·bo
/pləˈsēbō/
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noun
noun: placebo; plural noun: placebos

a harmless pill, medicine, or procedure prescribed more for the psychological benefit to the patient than for any physiological effect.
"his Aunt Beatrice had been kept alive on sympathy and placebos for thirty years"
a substance that has no therapeutic effect, used as a control in testing new drugs.
a measure designed merely to calm or please someone.

Interesting article below.  Imagine testing one vaccine against another - as a placebo? We've been fed two decades' worth of placebos from the pharma, medical and public health industries - "a measure designed merely to calm or please someone." Ironic that the vaccine industry's mask is slipping during this, the time of Covid and masks.

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Coronavirus vaccine: why it's important to know what’s in the placebo

September 21, 2020 7.14pm BST

Some researchers conducting clinical trials on a COVID-19 vaccine have not revealed to the public what the placebo contains, but they should. This is because the placebo ingredients influence how effective or harmful the active treatment, with which the placebo is compared, appears. Our new guideline published in PLOS Medicine remedies this problem by providing a template for reporting what’s in placebo controls.

In some COVID-19 vaccine trials, participants in the control group (the group receiving a placebo) are injected with a saline solution. In other trials, they receive an actual treatment. For example, in the COVID-19 vaccine developed by the University of Oxford, the control group receives a meningitis and septicaemia vaccine as a placebo.

The benefit of using an actual vaccine as the placebo control is that it will cause a similar reaction at the site of the injection as the COVID-19 vaccine, such as muscle pain and soreness. This prevents patients from knowing whether they are getting the placebo or the real treatment. The scientific term for hiding knowledge of who got what treatment is “blinding”.

If patients know they are getting the real thing, they may expect to get better, and their expectations can make them get better a bit faster. And if they know they are getting the placebo, they could drop out of the trial because they know they aren’t getting the actual treatment. Adding an actual vaccine to the placebo control helps the trial remain blinded and so prevents bias arising from differing expectations.
Active placebos

The main problem with including something active in the placebo, such as another vaccine, is that it can confuse researchers when they measure side-effects.  Read more here.