More than two-thirds of the common side effects people experience after a Covid jab can be attributed to a negative version of the placebo effect rather than the vaccine itself, according to researchers.
The nocebo effect accounted for almost 76% of all common adverse reactions after the first dose and nearly 52% after the second dose, according to scientists in the US.
The findings suggest that a significant proportion of milder side effects, such as headaches, short-term fatigue, and arm pain, are not produced by the vaccine, but by other factors thought to trigger the nocebo response, including anxiety, expectation and misattributing various ailments to having had the jab.
The researchers argue that better public information about nocebo responses may improve Covid vaccine uptake by reducing the concerns that make some people hesitant.
Ted Kaptchuk, a professor of global health and social medicine at Harvard Medical School, said that patients told that the intervention they are taking has side-effects that are similar to placebo treatments for the condition in randomised controlled trials. We need more research. Kaptchuck and Dr. Julia Haas at the Beth Israel Deaconess Medical CenterIsrael Deaconess Medical Center in Boston examined adverse events reported during a dozen clinical trials of Covid vaccines. In each trial, the participants in the placebo arm were given injections of inactive salt solution instead of vaccine. The study did not look at rare side effects, such as blood clots or heart inflammation.
The researchers describe how more than 35% of those in the placebo groups had systemic side effects, such as headache and fatigue, with 16% reporting site-specific ailments such as arm pain or redness or swelling at the injection site.
As expected, those who received a first shot of vaccine were more likely to experience side effects. About 46% reported systemic symptoms and two-thirds experienced arm pain or other localised symptoms at the injection site.
When the researchers looked at side effects after the second jab, they found that the rate of headaches or other systemic symptoms was nearly twice as high as in the vaccine group compared to the placebo group, at 61% and 32% respectively. The difference was even greater for local ailments, reaching 73% among those who had the vaccine and 12% in the placebo group.
The researchers found that about two-thirds of the common side-effects reported in Covid vaccine trials are caused by the nocebo effect, in particular headaches and fatigue, which many Covid vaccine leaflets list as the most common adverse reactions after a shot.
Kaptchuk argues for more information about side-effects, not less, because evidence shows that information about side-effects can cause people to misattribute common ailments to the vaccine, or make people hyper-alert to how they are feeling. Most researchers believe that patients should be told less about side effects to reduce their anxiety. I think this is wrong.