The hantavirus outbreak that has killed three people and put 12 countries on alert is less contagious than COVID and likely won’t turn into a major pandemic, a leading hantavirus researcher told The Post.Officials are scrambling to track and potentially quarantine people who may have been exposed to a rare, human-to-human strain of hantavirus aboard an Atlantic cruise ship, including at least six Americans.Hantavirus — which normally spreads via mouse droppings and killed Gene Hackman’s wife last year — has