Intense fatigue, headaches, chills, body aches… regardless of the vaccine administered against Covid-19, many patients have already encountered these post-injection side effects. An American study, published on January 18 in the journal jama-network, yet indicates that most of these adverse effects would be linked to the nocebo effect, not to the vaccine itself (source 1).
What is the nocebo effect?
The nocebo effect consists of the exact opposite of the placebo effect. The Larousse dictionary defines it as “lappearance of benign adverse effects, mainly of psychological origin, after administration of a drug that is inactive or that cannot itself produce these effects” (source 2). In other words, some people would anticipate the side effects of the vaccine against Covid-19 so much that they would feel them no matter what. come.
To measure the extent of this phenomenon in people newly vaccinated against Covid-19, the scientists took into account the reports of adverse effects from 45,000 volunteers involved in twelve clinical trials of vaccination against Covid-19. All vaccines were thus 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 effects occurring after the first injection of a real vaccine are linked to this nocebo effect. The same is true for 52% of the reactions occurring after the second injection.
The role of stress and anxiety
The researchers point out that the side effects experienced after the vaccine are less related to the content of the active substance than to stress and anxiety. As proof, the rate of reported adverse effects would decrease for the second injection, because the patients would be less stressed and would have more confidence in the vaccine.
The study thus concludes that more than half of the side effects appear because one expects to feel them.
She advocates information transparency and emphasizes the importance of trust between patients and staff authorized to vaccinate.