While some side effects of COVID-19 vaccines are real, others may be due to the nocebo effect, a negative psychosomatic reaction to a harmless treatment.
Even before they hit the market, many people were afraid of COVID-19 vaccines, mainly because of the side effects they might cause. Family, friends, and colleagues discussed their condition in the days following the first and second injections. Some felt almost nothing, just pain in their arm, while others were bedridden for three days, tired and sore, even with a fever. Fear of a bad reaction to the vaccine is one of the main reasons why a minority of the population refuses vaccination.
But while everyone’s experiences are real, their connection to COVID-19 vaccines may not be so clear. In clinical trials, the group that received an inert placebo, such as saline, also experienced side effects. This is the so-called nocebo effect, the opposite of the placebo effect.
Placebo and nocebo
The placebo effect is well known to the general public and is studied extensively by scientists. It occurs when a neutral intervention has positive effects on the patient’s health. A better mood, more energy, better well-being. A doctor’s reassuring words can also have a placebo effect. Without curing anything, the placebo effect can still improve the patient’s overall condition.
The nocebo effect is defined as follows: a harmless treatment, which when administered is accompanied by negative effects or exacerbation of certain symptoms due to negative expectations or the psychological state of the patient. Both phenomena are largely psychological but cause real symptoms: positive for the placebo effect, negative for nocebo.
76% of post-vaccination adverse events are psychosomatic in origin
A meta-analysis published in Jama Network Open looked at the proportion of adverse events attributable to the nocebo effect after COVID-19 vaccine injections. Scientists at Harvard Medical School examined 12 randomized clinical trials, conducted in volunteers over 16 years of age, that included a “vaccine” group and an “inert placebo” group for which follow-up of adverse events was available within seven days of injection.
The proportion of local and systemic adverse events was calculated for the vaccine and placebo groups for this series of publications. According to their results, 35.2% of those who received a first placebo injection reported a systemic adverse event, mainly fatigue, and headache; 31.8% after the second injection.
In comparison, 46.3 percent of those who received their first dose of COVID-19 vaccine reported the same type of symptoms; and 61.4 percent after the second dose.
The scientists found that 76% of the systemic side effects that occurred after the first injection of a Covid-19 vaccine were due to the nocebo effect, and 51.8% after the second dose.
Real local adverse reactions
The nocebo effect makes the vaccination more unpleasant than it really is. Not all side effects after vaccination are due to our fear or anxiety about vaccines. Local reactions are the result of the vaccine and its formula activating the immune system.
Only 16.2% of the volunteers in the placebo group reported a local adverse reaction after the first injection; 11.8% after the second injection. While 66.7% of the volunteers in the vaccination group showed a local reaction after the first dose and 72.8% after the second. Thus, 24% of the local adverse reactions were due to the nocebo effect after the first injection, 16.2% after the second.
So it is not just about psychology. However, discussing the nocebo effect or the possibility that no unpleasant side effects occur with the public could have a beneficial effect and reduce the occurrence of non-specific symptoms, such as fatigue and headache. “In addition, informing the public about a possible nocebo effect could help to reduce concerns about Covid vaccines, which could also reduce hesitation to vaccinate,” the study authors conclude.