The list of potential side effects from Covid-19 vaccines is long. But scientists now say many of the adverse reactions people have been feeling could be caused not by the vaccines themselves, but by the nocebo effect. This is when people anticipate a negative response to a medicine and then experience exactly that, even if they were given an inert substance. It’s the counterpart of the more familiar placebo effect, when people experience positive effects thanks to their positive expectations. According to research published in January, some three quarters (76 per cent) of complaints of physic…