The Swine Flu of 2009 was officially a pandemic. It spread widely enough and killed enough people to qualify, even though vaccination campaigns successfully reduced its potential impact. Some people have questioned the medical investment to counter the virus on the basis that it didn’t turn out to be as bad as predicted. That misses the whole point. The expense was worth it because it worked.
That year’s Influenza A virus subtype H1N1 is a beautiful thing. In an engineering sense, I mean. You can admire the way nature has put together an efficient and elegant machine. (The name comes from the variety of Hemagglutinin and Neuraminidase proteins in the outer shell. There are 16 H and 9 N subtypes, and this one has version 1 for both.)
Flu viruses have a genome consisting of eight separate sections of genetic information. The 2009 H1N1 has three genes from North American swine flu, two from Eurasian swine flu, two from North American bird flu, and one from human flu, the latter being specifically from the H3N2 strain that came from South East Asia in the 1993 flu season.
So H1N1 is a custom virus, the swine flu genes code for its outer shell, and the human and avian flu genes for its replication abilities. I’m not suggesting that it was put together in a laboratory: it almost certainly put itself together in a pig. Probably a North American pig. Because when a cell gets infected with two different flu viruses at once, the viral replication almost inevitably creates mixed offspring.
The famous flu pandemic of 1918 was also caused by a type of H1N1 which had acquired alternative genes, although the exact specifics are still being researched. In that case, the outer protein shell was of avian flu origin; inside there was at least one human flu gene; and possibly a swine flu gene.
H1N1 of 1918 is estimated to have killed about 20% of humans that it infected, or about 5% of the world’s population: maybe about 100 million people. Initially though, it was not very lethal. There was a first wave of infections in the Northern Hemisphere Spring which was similar to an ordinary flu outbreak. But by Autumn, the virus had evolved, either by random mutation or by acquiring a new, swapped gene from another sister virus.
In the second wave, the virus had acquired the ability to over-drive the victim’s immune system. almost like a massive allergy attack. Most people actually died from secondary infections in their lungs caused by excess fluid as their immune systems overwhelmed their bodies, but there were other interesting symptoms, such as bleeding from the nose, ears, stomach, and intestine. Unusually, the majority of fatalities all round the world were in young, healthy people, because their vigorous immune systems were powerful enough to kill them when turned loose by the virus.
Because the second wave virus was a mutated descendant of the first, the people who had suffered “normal” flu in the first wave were immune to the second, but as you probably know, the virus mutates so swiftly that you need a new vaccination every year.
Swine flu is still circulating, and still mutating. This year, 297 Americans contracted the H3N2 strain from pigs, mostly at agricultural fairs. One person died. In a separate outbreak, three people in Minnesota were infected with H1N2. Interestingly, both strains of the virus carry the same human gene which made the 2009 pandemic so infectious. So does a different variety of H1N2 found in Korea.
So far, most research has taken place on the Korean virus, and it has turned out to be unusually infectious and virulent. It is likely that the two American ones are as well, but it has been claimed that testing has been hindered by the reluctance of the American agricultural industry to accept that there is a problem and to engage with it.
The 2009 pandemic probably started in North America. The 2012/13 one probably will as well.