A study conducted by researchers at Beth Israel Deaconess Medical Center in the United States found that adverse effects after the Covid-19 vaccine were psychological in more than two-thirds of clinical trial volunteers.
The nocebo effect – as opposed to placebo – occurs when an individual experiences unpleasant reactions that are not specifically related to a drug.
In the case of placebo, there are physical or psychological benefits without the person having taken a specific medication – it can be a flour pill or a saline injection, for example.
The study was published this Tuesday (18) in the Journal of the American Medical Association ( JAMA Open Network ). The researchers analyzed data from 12 clinical trials of Covid-19 vaccines with a total of 45,380 participants.
As is customary, about half receive a saline injection (placebo) in most cases, and the other half receive the vaccine. Volunteers do not know what they took until the end of the study.
The results show that 35% of participants who took a placebo injection reported adverse effects after the first dose – mainly body pain, fever and tiredness.
In the vaccine group, 46% reported experiencing some systemic adverse effect as reported above.
Members of the Placebo Studies Program at Beth Israel Deaconess Medical Center performed analyzes and calculations and were able to estimate that the nocebo effect was present in 76% of all adverse reactions among those who took the vaccine.
In the second dose, there were fewer reports of adverse effects, which led the researchers to suspect that the study participants had already anticipated, eventually even taking medication before symptoms appeared.
“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 fact sheets,” the director of the Program of Studies on Cancer said in a statement. Placebo and senior author of the study, Ted J. Kaptchuk.
He adds that “this type of information can cause people to misattribute common everyday sensations as stemming from the vaccine or cause anxiety and worry that make people hyperalert to bodily sensations about adverse events.”
Even so, Kaptchuk reinforces the ethical importance of reporting all possible adverse reactions associated with vaccines.
“Medicine is based on trust. Our findings lead us to suggest that informing the public about the potential for nocebo responses may help reduce Covid-19 vaccination concerns, which may lessen vaccination hesitancy,” concludes the researcher.
The package inserts of anti-Covid vaccines bring as common adverse reactions pain at the site of application, fatigue, fever, muscle and headaches, nausea, among others. It should be noted that all of them are usually mild and resolve on their own by the next day.
These effects, experts say, should not be used as a justification for discouraging vaccination. Covid-19 is a disease that can lead to death, especially unimmunized individuals.