‘Nocebo effect’: two-thirds of Covid jab reactions not caused by vaccine, study suggests

A negative version of the placebo effect is what causes more than two-thirds of the common side-effects people experience after a Covid jab, according to researchers.

After the first and second dose of Covid vaccines, the "nocebo effect" accounted for about 75% of all adverse reactions, according to data from 12 clinical trials.

The findings suggest that a lot of the milder side-effects, such as headaches, short-term fatigue, and arm pain, are not produced by the vaccine's components, but by other factors.

The researchers believe that better public information about nocebo responses may improve Covid vaccine take up by reducing the concerns that make some people hesitant.

Ted Kaptchuk, professor of global health and social medicine at Harvard medical school, said that telling patients that the intervention they are taking has side-effects that are similar to placebo treatments for the condition in randomised controlled trials actually reduces anxiety and makes patients take a moment to consider the side- We need more research.

The adverse events reported during the Covid vaccine trials were analysed by Kaptchuck and Julia. The placebo arm was given injections of inactive salt solution instead of vaccine. The study didn't look at the rare side-effects of blood clot and heart inflammation.

More than a third of those in the placebo groups experienced so-called "systemic" side-effects, such as headaches and fatigue, with 16% reporting site-specific ailments.

The people who received a first shot of vaccine were more likely to experience side-effects. More than half of the people who reported symptoms at the injection site reported systemic symptoms.

The vaccine group had a higher rate of headaches than the placebo group, at 61% and 32%, when the researchers looked at side-effects after the second jab. The difference was greater for local ailments, with those who had the vaccine and those who didn't, reaching 73% and 12%, respectively.

The nocebo effect is the most common adverse reaction reported in Covid vaccine trials, accounting for about two-thirds of the common side-effects.

Kaptchuk argues that more information about side-effects is needed, not less, as evidence suggests that information about side-effects can cause people to misattribute common ailments to the vaccine. Patients should be told less about side-effects to reduce their anxiety, according to most researchers. I don't think this is right. Honesty is the way to go.