With the Northern hemisphere flu season just around the corner, health officials are wondering whether a new flu will pop up in an old form. Avian (bird) flu had been eliminated in most of 63 countries when it last hit a peak, in 2006, health officials told the BBC. But the number of cases has been rising again since 2008, appearing in poultry or wild birds that previously had been virus-free. Plus, it’s showing signs of having side-stepped vaccines with a new mutant strain.