The "nocebo effect" accounted for more than two-thirds of the common side effects people experience after a COVID-19 vaccination rather than the vaccine itself, according to a new study.

But the "nocebo effect" occurs when a person experiences unpleasant side effects after taking a treatment with no pharmacological effects. That same sugar pill causing nausea, or that syringe full of saline resulting in fatigue.

Researchers at Beth Israel Deaconess Medical Center (BIDMC), in a new meta-analysis of randomised, placebo-controlled COVID vaccine trials, compared the rates of adverse events reported by participants who received the vaccines with those who received a placebo.

The findings, published in JAMA Network Open, showed that about one-third of clinical trial participants who received no vaccine or placebo reported systemic adverse advents like headache and fatigue.

The team analysed data from 12 clinical trials of COVID vaccines, which included adverse effects reports from 22,578 placebo recipients and 22,802 vaccine recipients.

After the first injection, more than 35 percent of placebo recipients experienced systemic adverse events -- symptoms affecting the entire body, such as fever -- with headache and fatigue most common at 19.6 percent and 16.7 percent, respectively.

After the second dose, it dipped to 32 percent.

After the first dose nocebo accounted for 76 percent of all adverse events in the vaccine group, while nearly 52 percent of the side effects were reported after the second dose.

Although the reason for this relative decline in nocebo effects cannot be confirmed, the researchers believe that the higher rate of adverse events in the vaccine group the first time may have led participants to anticipate more the second time.

While some researchers argue that patients should be told less about the potential side effects of a vaccine, Kaptchuk believes it is ethically necessary to fully inform participants.

(This story was published from a syndicated feed. Only the headline and picture has been edited by FIT)