You are surely familiar with the famous “placebo” effect, when a substance containing no active ingredient can improve the health of certain patients. But do you know the “nocebo” effect? The latter is currently being widely discussed, in connection with vaccination against COVID-19. Let's start by recalling what it is: the appearance of undesirable effects after administration of a substance which seems harmful to the patient even if it is harmless. A real-world example of a nocebo effect is a person who receives a medication and doesn't feel well right after reading about its possible side effects.
For example, a sugar tablet can cause nausea while a syringe filled with saline solution can cause fatigue. Consider the nocebo effect as the negative version of the placebo effect, with the power of suggestion in common. But what is the connection with COVID vaccines? In clinical trials, researchers noted that people given an injection without knowing it was a placebo reported at least one adverse effect. These could be symptoms affecting the whole body, such as headaches, or a local event such as redness at the injection site.
The team came to the conclusion that this nocebo effect represented 76% of the adverse effects after the first injection of the Covid vaccine. The cause therefore is the stress felt more than the content of the vaccine itself. This explains why the rate of reported adverse effects was lower during the second dose, when patients were more confident. Be careful though, it's not all a question of psychology since certain mild effects have been reported by the drug agency. Even better, according to the researchers, is to inform the public of the existence of this nocebo effect to further reduce concerns about anti-Covid vaccines.
 Alexandra Bresson
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27/01/2022 | 
