A sore arm, headache, fatigue, nausea, dizzy spells, aching joints and sore muscles. These are the common side-effects reported by some of the 15 million NHS patients to get their first dose of a Covid-19 vaccine, as well as the 500,000 or so who have had their scheduled second dose. But rather than being something to dread, they could show you the vaccine is actually working. A study in December by Imperial College London found that almost a third of UK adults had concerns about Covid vaccine safety. Yet having these mild, temporary side-effects after the jab could be a good thing — a sign that the vaccine is already getting to work