A rare flu variant that has shown some resistance to the most commonly used antiviral treatment has been detected in at least two people in the United States, according to the US Centers for Disease Control and Prevention. Influenza viruses are constantly changing, but this variant has two concerning mutations in places that could lower the effectiveness of treatment with oseltamivir phosphate, known by the brand name Tamiflu. “There’s active global surveillance going on looking for these mutations,” said Dr. Andy Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health. “We want to know when they come...