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.
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
