Up to three quarters of all slight side effects after a Corona vaccination can be explained by the nocebo effect: the expectation of pain or discomfort means that both actually occur. 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 effects of the nocebo effect. According to the prescribed procedure, only half of the subjects in these studies are injected with the real vaccine – the other half, the control group, receives a saline solution in the 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 mild side effects occurred in the actually vaccinated subjects and how often the apparently vaccinated subjects complained of side effects.
The nocebo effect appeared most clearly after the first vaccination dose. 46 percent of those actually vaccinated had reported so -called systemic side effects such as fatigue or headache and 35 percent of the 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 are due to him. "Local side effects" at the injection site, on the other hand, are less often triggered by the nocebo effect. According to the data, he seems to be behind only 24 percent of the reported pain in the arm after the first vaccination.
After the second vaccination dose, the nocebo effect was less pronounced, obviously because of the second vaccination there are statistically more frequent side effects. At 32 percent, almost as many control group patients complained about symptoms as in the first run, but 61 percent in the actually vaccinated ones. Accordingly, after the second dose, only half of the side effects can be explained with the nocebo effect and not three quarters like after the first vaccination date.
The research group has published all its results in the journal "JAMA Network Open". An important trigger for the Nocebo effect is the knowledge that corresponding complaints can often occur after a vaccination - after all, every person willing to vaccinate is confronted with this information in the preliminary discussion. Would the nocebo-related side effects become rarer if patients were deprived of this information? In a press release, the head of the research group Ted Kaptchuk warns against such an approach as ethically unacceptable: "Medicine is based on trust," Kaptchuk is quoted in it. However, educating the public about the effect of the Nocebo effect could help to reduce a widespread fear of the corona vaccination.
The group has not examined the heavy but rarer side effects that have been observed in connection with some Covid 19 vaccines. Heart muscle inflammation or blood clotting disorders that occasionally occurred after vaccinations are not triggered by the nocebo effect.
