Home science Pain after covid vaccination may be in your head

Pain after covid vaccination may be in your head

Pain after covid vaccination may be in your head

A new study proves the power of the human spirit. According to this scientific work by a team of researchers from Beth Israel Deaconess Medical Center (BIDMC) from Boston, a large part of the adverse effects that occurred after the Covid-19 vaccination would be due to the nocebo effect. The latter is the evil twin of the placebo effect: a person feels negative effects from the treatment because they expect it.

The researchers conducted a meta-analysis of twelve randomized, placebo-controlled clinical trials of COVID-19 vaccination. Their results indicate that up to 64% of adverse effects experienced by patients can be attributed to the nocebo effect.

How did the team do that? The scientists looked at studies that included a total of 45,380 patients. Among them, 22,802 received a real vaccine, and the rest, or 22578 people, were given a placebo – a substance without active ingredients. None of the participants knew whether or not they had already received a vaccine.

Everything (or almost) is on our mind

After the first injection, researchers found that 46.3% of patients who had already been vaccinated reported it Systemic adverse effects It affects the whole body – mainly headaches and fatigue – and that 66.7% reported local adverse effects, such as pain or swelling at the site of the bite. As for the placebo-treated patients, 35.2% reported systemic effects and 16.2% localized effects. After comparing the ratios between the two groups, the team concluded that the effect of nocebo represented up to 76% of systemic adverse effects and 24% of local adverse effects after the first vaccine dose.

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However, the effect of nocebo weakens during the second injection. In fact, placebo-treated patients were less likely to report adverse effects: 31.8% for systemic effects and 11.8% for topical effects. Whereas in vaccinated subjects, adverse effects increased: 61.4% reported systemic effects and 72.8% local effects. Thus, during the second injection, only 52% of the adverse effects were due to the nocebo effect.

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For the team, these results are good news. “Collecting systematic evidence about nocebo responses in vaccine trials is important for Covid-19 vaccination worldwide, particularly because concern about side effects will be cause for reluctance to do so,” says BIDMC researcher Julia W. Haas. Thus, informing patients of the effect of nocebo can help reduce adverse effects, particularly headache and fatigue, symptoms that are highly sensitive to the effect of nocebo.


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