Fatigue, pain, fever: mild side effects often occur after vaccination. But often the vaccine itself is not responsible for this, but the unconscious expectation of the vaccinated person. FITBOOK explains what the nocebo effect is all about.
You are tired, you feel weak and you have a headache. But what is interpreted as typical side effects of a corona vaccination are often not vaccination reactions, but the result of the so-called nocebo effect. Up to three quarters of all mild side effects after a corona vaccination can apparently be explained by the nocebo effect. This was the result of the systematic evaluation of twelve studies that has now been published in the specialist journal «JAMA Network Open».
What is the nocebo effect?
The nocebo effect is the opposite of the placebo effect, in which patients experience a positive effect after a sham treatment. The opposite is the case with the nocebo effect. Instead of expecting an improvement after taking a drug, patients fear feeling a negative effect – which then also occurs. Thus, the condition for the emergence of this effect is the knowledge of the possible harmful effects of a drug or therapy.1
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Nocebo effect in corona vaccinations
The nocebo effect was also observed in studies testing vaccines against corona. As prescribed, only half of the subjects in these studies are injected with the real vaccine. The other half just get a shot of saline. Of course, the participants do not know which group they are in.
Researchers at the Beth Israel Deaconess Medical Center in Boston compared the incidence of mild side effects in those who were actually vaccinated and those who were only ostensibly vaccinated. Of a total of 45,380 subjects over the age of 16, 22,578 received a «wrong» injection, the rest a real vaccination. The result: After the first vaccination dose, around 46 percent of those who were actually vaccinated complained about side effects such as tiredness and headaches. At the same time, 35 percent of those who only appeared to be vaccinated stated that they suffered from the same vaccination reactions. A classic nocebo effect. From the ratio of the two numbers, the researchers determined that up to 76 percent of the reported vaccination reactions are the result of the nocebo effect.2
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It was different with the second vaccination: Almost 32 percent of those apparently vaccinated complained about symptoms. In contrast, 61 percent of those who were actually vaccinated. In this respect, it can be assumed that after the second vaccination only half of the side effects can be attributed to the nocebo effect.
There was also a difference between systematic side effects such as headaches and fatigue and local side effects such as pain, redness or swelling at the injection site. Accordingly, local side effects were triggered less frequently by the nocebo effect. After the first vaccine dose, this appears to have been the case for only 24 percent.
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Impact of the nocebo effect on vaccination readiness
The nocebo effect presents doctors and medical professionals with a dilemma: on the one hand, they are obliged to inform the patient about possible side effects. But on the other hand, they could also harm him through the knowledge and the possibly occurring nocebo effect.1
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With their study, the researchers at the Beth Israel Deaconess Medical Center want to explain the frequency and occurrence of possible side effects. «Adverse events after placebo treatment are common in randomized controlled trials,» says the study’s lead author, PhD Julia W. Haas, in a press release. «Gathering systematic evidence of these nocebo responses in vaccine trials is important for COVID-19 vaccination worldwide, particularly as concerns about side effects are reported to be a reason for vaccination reluctance.»3
Lead author Ted J. Kaptchuk, director of the Placebo Trials Program at Beth Israel Deaconess Medical and Professor of Medicine at Harvard Medical School, is clear: “Medicine is based on trust. Our results lead us to believe that educating the public about the potential for nocebo reactions could help reduce concerns and anti-vaccination about COVID-19.”3