"In one sense, it's one of the mildest shifts because most people on the planet have got some memory, have come across H1N1 viruses since 1978," Oxford says.
Even though health officials are calling this new virus H1N1, that's also the type of virus that's in wide circulation today. And it has an interesting history. It was the dominant flu virus through the 1920s, '30s and '40s. Oxford says it disappeared in 1957, when it was displaced by another flu virus. But then a strain of H1N1 suddenly reappeared in 1977.
"Now where could it have come from?" he asks. "We reckon now, in retrospect, it was probably released accidentally from a laboratory, probably in northern China or just across the border in Russia, because everyone was experimenting with those viruses at the time in the lab."
It was nothing malicious, Oxford believes, just some flu vaccine research that broke out of containment. The descendents of this virus are still circulating. He notes that most people who have encountered the newly emerged H1N1 virus seem to have developed only mild disease, and he speculates that's because we have all been exposed to a distant cousin, the H1N1 virus that emerged in the 1970s.
"That escaped virus perhaps will provide some benefit now in the face of this pig thing," Oxford says...More at link