Up to three quarters of all mild side effects after a corona vaccination can be explained by the nocebo effect: the expectation of pain or discomfort leads to both actually occurring. It is the counterpart to the placebo effect, in which those affected expect an improvement.
This is the result of a systematic evaluation of twelve studies in which common corona vaccines were tested. Such studies are excellent for observing the workings of the nocebo effect. Because according to the prescribed procedure, only half of the test persons in these studies are injected with the real vaccine – the other half, the control group, receives a saline solution in their arm for comparison. The participants do not know which group they are in.
A research group led by Julia W. Haas from the Beth Israel Deaconess Medical Center in Boston has now compared how often the subjects who were actually vaccinated had minor side effects and how often the subjects who only appeared to be vaccinated complained about side effects.
The nocebo effect was most evident after the first vaccination dose. 46 percent of those actually vaccinated had reported so-called systemic side effects such as tiredness or headaches and 35 percent of those apparently vaccinated. The extent of the nocebo effect is calculated from the ratio of the two numbers.
As a result, Haas and colleagues calculated that around 76 percent of the reported side effects can be attributed to him. “Local side effects” at the injection site, on the other hand, are triggered more rarely by the nocebo effect. According to the data, it seems to be behind only 24 percent of reported arm pain after the first vaccination.