STOCKHOLM—Sweden’s King Carl XVI Gustaf and Queen Silvia have tested positive for COVID-19, the palace said in a statement on Tuesday. “The King and Queen, who are fully vaccinated with three injections, have mild symptoms and are feeling well, given the circumstances,” the palace said in a statement. The palace said the king, 75, and the queen, 78, were self-isolating and that work to trace those they had been in contact with was underway. Carl Gustaf, whose role is largely ceremonial, became Sweden’s head of state at the age of 27, following the death of King Gustaf VI Adolf in 1973, and is the country’s longest serving monarch. Crown Princess Victoria, his eldest daughter and heir to the throne, had the coronavirus in March last year as did her husband, Prince Daniel. Both recovered after suffering mild symptoms. The Omicron variant of the virus has spread fast, especially in urban …