Two-thirds of negative reactions to anti-covid vaccines are caused by the “nocebo effect”

The journal Jama Network Open published a study of American doctors who studied adverse reactions to anti-coronavirus vaccines, reports The Guardian. Scientists analyzed the results of 12 clinical trials of vaccines and found that most of the negative reactions to the injection are caused by the so-called “nocebo effect”. Nocebo is the opposite of placebo: it is a drug that does not have a real pharmacological effect, which causes a negative reaction in the patient. Like the placebo effect, the nocebo effect is the result of a psychophysiological response.

In clinical trials of vaccines that doctors studied, people in the placebo group were given saline instead of the vaccine. After the first injection, more than 35% of participants in the placebo groups experienced so-called systemic side effects such as headache and weakness, and 16% reported local reactions - pain in the arm or redness and swelling at the injection site. Those who received the vaccine, as expected, experienced side effects more frequently, with 46% reporting systemic symptoms and two-thirds experiencing arm pain.

After the second injection in the vaccinated group compared with the placebo group, the frequency of headaches or other systemic symptoms was almost twice as high - 61% and 32%, respectively. Local reactions were experienced by 73% of the vaccinated and 12% of the placebo group.

Overall, it is estimated that about two-thirds of the common side effects reported in vaccine trials were due to the nocebo effect. Among these reactions are headache and fatigue, which are among the most common adverse reactions after vaccination.