Up to three quarters of side effects caused by the Covid vaccine may be ‘all in the head’, experts say.
Millions of people across the world claim to have suffered headaches, tiredness and even diarrhoea after getting jabbed.
But scientists at Harvard believe the vast majority of the effects are due to the ‘Nocebo’ effect, a phenomenon when someone faces an uncomfortable side effect from a jab simply because they expected to.
In the study, scientists pored over reports from 44,000 people on the side effects they claimed to have experienced after getting jabbed.
But half of the participants were not told they had actually been given a placebo, or fake vaccine — such as a saline solution.
The researchers said many side effects people claimed were due to jabs were likely actually triggered by ‘background sensations’ not linked to jabs.
They said that anxiety about vaccines had made people ‘hyper-alert’ to their bodies, leading many to link unrelated issues to the vaccine.
The above graph shows the proportion of trial participants that got the Covid vaccine which reported experiencing side effects from the jab. 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 likely not due to the jabs (striped areas)
In the study, researchers analysed the rates of side effects in around 22,000 people that were given the Covid vaccine in clinical trials.
This was compared to a control group of roughly the same size that was given the fake vaccine.
Placebos are a routine part of clinical trials, and are used to establish whether a treatment is working.
What is the placebo and nocebo effect?
Studies normally include placebo groups to help test a treatment.
In Covid vaccine trials, these volunteers were not told they were receiving a fake treatment — or saline solution — in the place of a vaccine.
They were also treated exactly the same way as the vaccinated group, meaning they also received two doses of the solution via an injection.
Scientists include the group to help work out if a treatment is working and to cancel out the placebo and nocebo effects.
In the placebo effect, someone is more likely to report a positive outcome because they had positive expectation.
On the other hand, the nocebo effect is when someone 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 likely affected vaccine trials.
Results showed that in the vaccinated group, 46 per cent said they suffered adverse effects like a headache or exhaustion after the first dose.
This rose to 61 per cent of the group after the second jab.
A total of 66 per cent also mentioned local reactions such as pain, swelling or redness after the first jab.
Similarly the number of reactions reported also ticked up after the second dose, reaching 73 per cent.
But the opposite was seen in the placebo group.
Roughly a third of participants in this group reported adverse effects such as a headache, with the proportion dropping slightly after the second dose.
This pattern was repeated for local reactions around the injection site, which fell from 16 to 12 per cent by the second jab.
The scientists said it was possible for someone in the placebo group to say they had suffered a reaction to a vaccine despite not actually being given the vaccine because they were expecting to.
Similarly, it was possible for people who were given the jab to say they had faced a negative effect even if one didn’t actually happen.
This is called the nocebo effect, and is when someone says they suffered a negative reaction to a treatment just because they believed they would.
In order to suggest what proportion of side effects in jabbed people were likely not due to the vaccine the scientists calculated a ratio.
They compared the rates of side effects in the vaccine group to those in the placebo group to work out how many were genuinely triggered by the jab.
They estimated 76 per cent of all headaches, fatigue and other adverse events reported after the first dose were down to the nocebo effect.
But this dropped to 52 per cent after the second dose.
Scientists said the proportion of genuine side-effects from the jab rose after the second dose because the immune system was fired up.
And for reactions around the injection site they said 25 per cent were likely not due to the vaccine after the first dose, compared to 16 per cent after the second.
Scientists said people in the placebo group reported fewer reactions after the second dose because they had been less likely to experience one after the first jab.
This, they argued, made them less concerned about suffering a reaction when they got their second jab and, therefore, less likely to report one.
Professor Ted Kaptchuk, a world-renowned expert in the placebo effect who was involved IN the research, said it was clear negative expectations were leading to some ‘side effects’ being wrongly attributed to the vaccines.
He said: ‘Nonspecific symptoms like headache and fatigue — which we have shown to be particularly nocebo sensitive — are listed among the most common adverse reactions following Covid vaccination in many information leaflets.
‘Evidence suggests that this sort of information may cause people to misattribute common daily background sensations as arising from the vaccine.
‘Or [it could] cause anxiety and worry that makes people hyper alert to bodily feelings about adverse events.’
The study was published in the journal JAMA Open Research.
It included jabs made by AstraZeneca, Pfizer and Moderna — all in used in the UK.
It also included the Johnson and Johnson jab, which is being used in the US but not in the UK, and some vaccines that were still in trials.
Clinical trials always include placebo groups in order to establish whether the trial treatment has any impact.
Volunteers given sugar pills or saline injections are treated in exactly the same way to the group receiving the actual treatment.
In Covid vaccine trials placebo groups were double-blind — meaning neither they or the scientists administering the vaccines knew who was getting the actual vaccine.
Britain’s health regulator lists headaches and fatigue as common side effects of being inoculated, which affect around one in 10 people who get the jab.
The MHRA has received more than 1.4million reports of side-effects since the roll out began out of more than 50million doses dished out.
But many complaints are for conditions including ear problems, eye problems and indigestion, which have never been linked to the vaccines.
The same data has, however, also allowed regulators to spot blood clots and other rare side effects by determining what complications are occurring more often than expected.