According to an American study published on January 18 in the journal Jama Network, 76% of the side effects experienced after an injection of vaccine against Covid-19 are linked to the nocebo effect, the harmful alter-ego of the placebo effect.
In other words, the majority of patients would experience adverse effects, most often mild, because they expected them. As part of the vaccination against Covid-19, patients generally complain of intense fatigue, headaches, chills, body aches… unpleasant effects which would actually be caused by the nocebo effect.
A study conducted on 45,000 volunteers
To measure the extent of this phenomenon, scientists took into account reports of adverse effects from 45,000 volunteers involved in twelve clinical trials of vaccination against Covid-19. Thus, all vaccines were included in the study. One group of participants actually received a dose of the vaccine, while the other received a placebo. Results? A number of people who received a neutral product still experienced side effects after the injection. Data analysis has allowed scientists to state that 76% of adverse reactions after the first injection of a real vaccine are related to the nocebo effect.
Fewer side effects with the second dose
The researchers point out that the side effects experienced after the vaccine are therefore less related to the content of the active substance than to stress and anxiety.
Moreover, the study shows that the rate of adverse effects would decrease with the second injection, because the patients would be less stressed and would have more confidence in the vaccine.