More than two-thirds of the common side-effects people experience after a Covid jab can be attributed to a negative version of the placebo effect rather than the vaccine itself, researchers claim.

Scientists in the US examined data from 12 clinical trials of Covid vaccines and found that the “nocebo effect” accounted for about 76% of all common adverse reactions after the first dose and nearly 52% after the second dose.

The findings suggest that a substantial proportion of milder side-effects, such as headaches, short-term fatigue, and arm pain are not produced by the constituents of the vaccine, but by other factors thought to generate the nocebo response, including anxiety, expectation and misattributing various ailments to having had the jab.