Up to three-quarters of side effects caused by Covid vaccine could be due to ‘nocebo’ effect
Up to three-quarters of side effects caused by the Covid vaccine may be ‘all in the head’, experts say.
Millions of people around the world claim to have suffered from headaches, fatigue and even diarrhea after being bitten.
But Harvard scientists believe the vast majority of the effects are due to the “Nocebo effect”, a phenomenon when a person experiences an uncomfortable side effect of a jab simply because they expected it.
In the study, scientists looked at reports from 44,000 people of the side effects they claimed to have experienced after being bitten.
But half of the participants were not told that they had actually received a placebo or a fake vaccine, such as saline solution.
The researchers said that many of the side effects people claimed were due to the bites were likely actually triggered by “background sensations” unrelated to the bites.
They said vaccine anxiety has made people “hyper-alert” to their bodies, leading many to link issues unrelated to the vaccine.
The graph above shows the proportion of trial participants who received the Covid vaccine who reported experiencing side effects from the vaccine. These results were compared to reports of side effects in the placebo group. A ratio of side effects reported in the placebo and vaccinated group was then calculated. This allowed scientists to determine what proportion of side effects in the vaccinated group were probably not due to the bites (striped areas)
In the study, researchers analyzed side effect rates in around 22,000 people who received the Covid vaccine in clinical trials.
This was compared to a control group of about the same size who received the fake vaccine.
Placebos are an integral part of clinical trials and are used to determine if a treatment works.
What is the placebo and nocebo effect?
Studies normally include placebo groups to help test a treatment.
In the Covid vaccine trials, these volunteers weren’t told they were getting a fake treatment – or a saline solution – instead of a vaccine.
They were also treated in exactly the same way as the vaccinated group, meaning they were also given two doses of the solution by injection.
Scientists include the group to help determine if a treatment is working and to negate placebo and nocebo effects.
In the placebo effect, a person is more likely to report a positive result because they had positive expectations.
On the other hand, the nocebo effect occurs when a person is more likely to report a negative outcome because they had a negative expectation.
Professor Ted Kaptchuk, a world-renowned expert on the placebo effect, said these vaccine trials likely affected.
The results showed that in the vaccinated group, 46% said they experienced adverse effects such as headaches or exhaustion after the first dose.
This figure rose to 61% of the group after the second hit.
A total of 66% also mentioned local reactions such as pain, swelling or redness after the first shot.
Similarly, the number of reported reactions also increased after the second dose, reaching 73%.
But the opposite was observed in the placebo group.
About a third of participants in this group reported adverse effects such as headache, with the proportion decreasing slightly after the second dose.
This pattern was repeated for local reactions around the injection site, which decreased from 16% to 12% on the second shot.
The scientists said it was possible for someone in the placebo group to say they had had a reaction to a vaccine when they didn’t get the vaccine because they expected it.
Likewise, it was possible for people who received the jab to say that they suffered a negative effect even though it hadn’t actually happened.
It’s called the nocebo effect, and it’s when someone says they experienced a negative reaction to a treatment simply because they believed they would.
In order to suggest what proportion of side effects in those bitten were probably not due to the vaccine, the scientists calculated a ratio.
They compared the rates of side effects in the vaccinated group to those in the placebo group to determine how many were actually triggered by the vaccine.
They estimated that 76% of all headaches, fatigue and other adverse events reported after the first dose were due to the nocebo effect.
But that figure dropped to 52% after the second dose.
The scientists said the proportion of actual side effects from the vaccine increased after the second dose because the immune system was activated.
And for reactions around the injection site, they said 25% were probably not due to the vaccine after the first dose, compared to 16% after the second.
The scientists said people in the placebo group reported fewer reactions after the second dose because they were less likely to have one after the first shot.
This, they argued, made them less worried about experiencing a reaction when they received their second hit and, therefore, less likely to report one.
Professor Ted Kaptchuk, a world-renowned expert on the placebo effect who was involved in the research, said it was clear that negative expectations led to certain “side effects” being wrongly attributed to vaccines.
He said: “Non-specific symptoms like headache and fatigue – which we have shown to be particularly sensitive to nocebo – are listed among the most common side effects after Covid vaccination in many leaflets of ‘information.
“Evidence suggests that this type of information may cause people to mistakenly attribute common daily background feelings as resulting from the vaccine.
‘Or [it could] cause anxiety and worry that makes people hyper-attentive to bodily feelings related to adverse events.
The study was published in the journal JAMA Open Research.
It included jabs made by AstraZeneca, Pfizer and Moderna – all used in the UK.
It also included the Johnson and Johnson jab, which is used in the US but not the UK, and some vaccines which were still in trials.
Clinical trials always include placebo groups to establish whether the treatment being tested has an impact.
Volunteers receiving sugar pills or saline injections are treated exactly the same as the group receiving the actual treatment.
In the Covid vaccine trials, the placebo groups were double-blind – meaning neither they nor the scientists administering the vaccines knew who was getting the actual vaccine.
The UK health regulator lists headaches and fatigue as common side effects of the inoculation, which affect around one in 10 people who receive the vaccine.
The MHRA has received over 1.4 million side effect reports since the start of the rollout from over 50 million doses distributed.
But many complaints relate to conditions such as ear problems, eye problems and indigestion, which have never been linked to vaccines.
However, the same data has also allowed regulators to spot blood clots and other rare side effects by determining which complications occur more often than expected.