Nocebo effect: two-thirds of Covid-19 reactions are not caused by the vaccine
The nocebo effect, a negative version of the placebo effect, is the responsible for more than two-thirds of adverse events attributed to the Covid-19 vaccine.
Scientists at Beth Israel Deaconess Medical Center (USA) analyzed data from 12 clinical trials of Covid vaccines and found that the “nocebo effect” accounted for about 76% of all common adverse reactions after the first dose and nearly 52% after the second dose. The team’s findings are published in
«JAMA Network Open».
The findings suggest that a substantial proportion of milder side effects, such as headaches, short-term fatigue, and arm pain, are not
produced by the components of the vaccine, but by other factors that are believed to generate the nocebo response, including anxiety, anticipation, and misattributing various ailments to having received the needlestick.
The placebo effect is a well-known phenomenon that improves a person’s physical or mental health after taking a treatment with no pharmacological therapeutic benefit, for example, a sugar pill or a syringe filled with saline. Although the The exact biological, psychological, and genetic underpinnings of the placebo effect are not well understood., some theories point to expectations as the main cause, while others argue that unconscious factors embedded in the doctor-patient relationship automatically reduce the volume of symptoms.
But sometimes the effect placebo can also cause harm: is the nocebo effect, which occurs when a person experiences unpleasant side effects after taking a treatment without pharmacological effects. That is, that same sugar pill that causes nausea, or that syringe filled with saline solution that produces fatigue.
“Adverse events after placebo treatment are common in randomized controlled trials,” stated lead author Julia W. Haas. “Collecting the systematic evidence regarding these nocebo responses in vaccine trials is important for Covid-19 vaccination worldwide, especially as concerns about side effects are reported to be a reason not to get vaccinated.”
The 12 clinical trials analyzed included reports of adverse effects of 22,578 placebo recipients and 22,802 vaccine recipients. After the first injection, more than 35% of those who received the placebo experienced systemic adverse events (symptoms that affect the whole body, such as fever), with headache and fatigue being the most common at 19.6% and 16.7%, respectively. 16% of those given placebo reported at least one local event, such as injection site pain, redness, or swelling.
By comparison, after the first injection, 46% of those who received the vaccine experienced at least one systemic adverse event, and two-thirds of them reported at least one local event. Although this group received a pharmacologically active treatment, at least some of their adverse events are attributable to the placebo effect, or in this case, nocebo, since many of these effects also occurred in the placebo group.
The analysis suggested that nocebo accounted for 76% of all adverse events in the vaccine group and nearly a quarter of all reported local effects.
After the second dose, adverse events among the placebo group dropped to 32% reporting systemic events and 12% reporting local effects. In contrast, participants who received the vaccine reported more side effects, with 61% reporting systemic adverse events and 73% reporting local adverse events.
The researchers calculated that nocebo accounted for almost 52% of side effects reported after the second dose. While the reason for this relative decrease in nocebo effects cannot be confirmed, the researchers believe that the higher rate of adverse events in the first-time vaccine group may have led participants to anticipate more the second time.
“Nonspecific symptoms such as headache and fatigue, which we have shown to be particularly sensitive to nocebo, are listed among the most common adverse reactions following Covid-19 vaccination in many information leaflets,” added lead author Ted J. Kaptchuk.
“Evidence suggests that this type of information may cause people to mistakenly attribute common daily sensations as vaccine-derived or cause anxiety and worry that make people highly alert to bodily feelings about adverse events.”
While some researchers believe that informing patients about adverse effects can cause harm, Kaptchuk believes that it is ethically necessary to inform
“Medicine is based on trust”Kaptchuk concluded. “Our findings lead us to suggest that informing the public about the potential for nocebo responses could help reduce concerns about vaccination against Covid-19, which could decrease vaccination hesitancy.”