Hugh Pickens writes: "Swine flu is nothing new. The first virus in the US was isolated in 1930, and since then there has been roughly one human case in the country every year. The latest virus is more infectious than previous strains, but little else is known for sure — how often it kills, how swiftly, and even precisely what those who succumb die of. Most of the victims developed flu over a week or so, which progressed to severe and ultimately fatal pneumonia. There is no clear explanation of why the virus has killed only in Mexico and Mexican health officials do not have a clear idea how many people are infected more mildly, making it almost impossible to gauge how lethal the virus is. Fresh vaccines to combat the infection could take between four and six months, by which time the first wave of the disease could be over. In 1918, when Spanish flu killed tens of millions, there were two subsequent waves, which were far more lethal than the first. "Thirty-five to forty thousand people die per year in the US from the regular flu," says Dr. Louise M. Dembry, director of hospital epidemiology at Yale-New Haven Hospital. "It's not that it's a benign disease even in regular times.""