Two thirds of adverse reactions to the covid vaccine would be attributed to the placebo effect

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Get vaccinated and think about everything that can happen to us, headaches, fever, bad body... Medicine often seeks answers to the

. The role of autosuggestion when receiving the anti-Covid puncture has been the subject of an American study that puts on the table that

or to the way in which we believe that it will not affect .

The fatigue and chills she experienced when she was given the covid vaccine could have been an effect of

rather than a direct cause of the immunizer itself. Thus concludes a study, which is published in

, on the adverse reactions reported by participants in clinical trials with vaccines, some of the cases of pain, fatigue and discomfort in vaccinated people can be attributed to

, given that

.

Analytical work by

, a researcher at Beth Israel Deaconess Medical Center in Boston, suggests that this effect could account for

in the vaccine group after the

, and almost

of reports

;

that effect could also explain a quarter of all reported local effects.

The research provides evidence of a well-known

in clinical trials:

, when in reality they are being given a pig in a poke.

A reason to hesitate before the vaccine

Quantifying the placebo effect in the case of vaccines against covid is of special interest, in the words of the first author of the work,

, since it seems that "concern about side effects is a

to

".

The study authors note that although more participants in the trials who received the vaccine reported adverse reactions, almost

of the volunteers who received

also

adverse event.

The work is based on a

-analysis of

placebo-controlled trials of

against covid-19, with a total of

. Hence the potential placebo effect associated with immunizations, which they refer to as

" (alluding to the fact that they measure unpleasant and non-positive side effects, after taking a substance without pharmacological action).

After the

, more than 35% of those given a saline solution (placebo) experienced systemic adverse events (primarily headache and fatigue, at 19.6% and 16.7%, respectively).

16% of those who received placebo reported a local reaction (such as pain, redness or swelling at the site of infection).

Among those who did receive the vaccine, 46% experienced a systemic adverse reaction and two-thirds of them experienced at least one local reaction.

After the

adverse reactions in the placebo group were reduced to 32%, and local effects to 12%.

In contrast, participants who received the vaccine reported more side effects (61% reported more systemic adverse effects and 73% local).

The effect diminishes after the second dose

Always according to this work, the calculated nocebo effect went from 76% with the first dose to 52% with the second puncture.

Although the reason for this decrease cannot be confirmed, the researchers believe that in a first contact with the vaccine, the participants could have anticipated what was going to happen to them.

"

such as headache and fatigue, which we have shown to be particularly sensitive to nocebo, are

-19 vaccination in many fact sheets

," says lead author from the work Ted J. Kaptchuk.

This professor at the Harvard University School of Medicine also clarifies that "the evidence suggests that this type of information can make people

as derived from the vaccine or that influence the appearance of anxiety and worry that make them very alert to bodily sensations about adverse events.

, head of the Clinical Pharmacology Service at the University Hospital of La Princesa, abounds in this

: "In this trial it is observed that the most reported adverse effect is headache. It can hurt all of us from time to time and, especially , in a

such as vaccination or fear of covid. There are more patients who get a headache when they receive the vaccine than if they receive the placebo, but the fact of receiving a puncture that we anticipate as a vaccine also can produce it."

The pharmacologist also points out that in these studies a

of potential adverse reactions was made.

"On a daily basis after vaccination, the volunteers were asked to write down any symptoms", a fact that may influence the determination of the placebo effect.

The Hospital de La Princesa team, together with other Spanish hospitals, carried out one of the clinical trials included in this meta-analysis, specifically on the Ad26.COV2-S vaccine from the pharmaceutical company Janssen.

Also a researcher in those first trials with the anti-covid vaccine,

, coordinator of the Clinical Research and Clinical Trials Unit of the La Paz University Hospital (Madrid), comments that while they carried out their study, many volunteers "arrived with the idea of that if they got the vaccine, they had to have a fever. Actually, as has been shown, it's more likely not to have it."

Motivated by the fever

For Borobia, the term "nocebo" used by the authors of this meta-analysis does not capture well the

of the trial volunteers. "At a time of the pandemic when there were no vaccines yet, the volunteers presented to the study with the intention of receiving it, instead of the placebo; therefore,

, as a sign that they had been immunized."

However, the specialist denies that these signs (in the form of a headache or tiredness) should necessarily be interpreted as a

. "Vaccines against covid have a

that is within

compared to other vaccines studied. The reactions will depend on whether it is a first or second dose, or if the disease has passed, among other elements." And remember that in the meta-analysis that has just been published, in the group that received the first dose of the vaccine, more than half (54%) did not report any systemic symptoms.

He also considers the idea that the

is related to more reactogenicity wrong.

"We still don't have any studies that show us this," he says, and the clinical experience is

, "with the third dose, there are people who don't even know about it. Among other factors, it depends on the profile of the individual and the interval with respect to the second dose.

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