This Sunday, March 11, is the 100th anniversary of the outbreak of Spanish flu in 1918, when patient zero was diagnosed. Anniversary usually implies something good, but Spanish flu was anything but. Albert Gitchell, an Army cook at Fort Riley, Kansas, woke up on March 11, 1918, thinking he had a bad cold. He didn’t. Instead, he was “patient zero” in what is still the deadliest pandemic in human history, the Spanish flu. By the time the pandemic was over in 1919, it had killed between 20-50 million people according to the CDC, which is already a pretty big range of uncertainty, but Wikipedia goes for 50-100M. That was about 2-4 percent of the world’s population at the time. It's estimated that it affected a third of the world population. In the US, the average life expectancy was reduced by 12 years due to all the early deaths. Actually, it is most unlikely that Albert was really patient zero, probably others had it first. It remains unknown where it came from. Despite the name, it didn't come from Spain. The Spanish name came about because the world was still mostly fighting World War I, and censors in most countries suppressed how bad the epidemic was. Spain was neutral in the WWI (since the Spanish royal family had connections to both sides), and so the news wasn't suppressed, which gave the impression that it was especially bad in Spain (and the king also had it badly, although he recovered, which obviously made the news). Spanish flu, which is a form of the H1N1 virus, seemed to cause an overreaction of the immune system. Normal flu (and many diseases) tend to be worst in people with weak or compromised immune systems, like babies and old people. Spanish flu hit people with strong immune systems badly, killing people who were fit and well in their twenties and thirties. A lot of people came home having survived the WWI, only to die from Spanish flu. The flu was so bad that it actually killed more people than WWI. And WWI was already notable for the number of casualties—neither of my great aunts married because, as one of them told me, "in the space of a couple of years, every boy I knew was killed". Plus, in the only connection to electronics in this post, one of them later worked in the code-breaking unit at Bletchley Park during WWII, but even the existence of Bletchley Park was still a state secret when she died, so I only found out later. So do we need to worry that the 1918 virus is lurking in the environment and is going to come back and kill 4% of the world's population again today (that would be over 1/4 billion people). The CDC reckons it is unlikely: It is impossible to predict with certainly, but the probability of the 1918 virus re-emerging from a natural source appears to be remote. Influenza experts believe that a pandemic is most likely to be caused by an influenza subtype to which there is little, or no, preexisting immunity in the human population. There is evidence that some residual immunity to the 1918 virus, or a similar virus, is present in at least a portion of the human population. Since contemporary H1N1 viruses circulate widely and the current annual influenza vaccines contain an H1N1 component, a 1918-like H1N1 virus would not fit the current criteria for a new pandemic strain. What Does H1N1 Mean Anyway? It's not just H1N1, there are also H1N1, H1N2, H2N2, H3N1, H3N2...H10N7. There are four type of flu. No, not the HxNy ones I just mentioned, they are known as A, B, C, and D. Only cattle get D. It is the A viruses that are further subdivided into the HxNy classifications, based on two proteins on the surface of the virus called (there will be a test at the end of this post) the hemagglutinin and the neuraminidase. There are 18 different hemagglutinin subtypes (H1-H18) and 11 different neuraminidase subtypes. (N1-N11). The main ones affecting humans are H1N1 and H3N2. The flu vaccine you may get each winter includes these two viruses and some forms of the B virus, based on what seems to be around. There is apparently a widespread misunderstanding that the flu virus is some sort of viral equivalent of an antibiotic. It isn't, it only protects against flu, and only if it turns out that the variety that winter matches (or is close) to what the disease experts guessed and included in the vaccine. One reason that this year's flu has been so bad is that the most virulent variety was not included in the vaccine, so the vaccine only offered limited immunity. The picture at the start of this article is a photomicrograph of H1N1 flu virus. They are about 100nm in diameter. Just as a datapoint, 80nm is the limit for manufacturability of features on an integrated circuit with 193i lithography, and no double patterning, so that is pretty close to the size of a flu virus. The new viruses typically incubate in birds or pigs. Initially, they can't make it across to humans, so there is some economic impact on poultry and pig farming. If they manage to make it across to humans, one of two things might happen. The virus can also make it from human to human, meaning a pandemic is possible, or it cannot, meaning that only people working with birds and pigs are likely to get it. The 2009 pandemic of swine flu was the second H1N1 pandemic (the first being the 1918 Spanish flu) and could be passed from human to human. Again, it affected mostly healthy people, not old people, As with the 1918 flu, there seems to be a lot of variation in estimates of how many people were killed, with the WHO initially going for 18,000 but cautioning that it is "unquestionably higher". Then, more recent research went for 579,000 (32 times higher) and the "experts'" latest number is 285,500 (I don't think they stayed awake in the lecture on not putting more significant digits in a number than the accuracy of measurement can justify). And another PSA, you can't get swine flu from eating pork or bacon. The recent version of H7N4 in Asia could be transmitted from birds to birds, and birds to humans (so people working with poultry might get it), but it was not transmissible from human to human, which is obviously a pre-condition for a major pandemic. But there was no way to tell that except by noticing that other humans didn't seem to get it, hence there was somewhat of a panic at the time, with stockpiling of Tamiflu. In fact there is something of a minor panic to get Tamiflu now, due to the bad flu season this winter, with prescriptions running over 10X what they did last year (and there is a lot of doubt about whether it does any good anyway). One year's flu virus is usually pretty similar to the previous years, so even without flu vaccine, there is quite a lot of residual immunity in the human population, meaning a pandemic cannot take hold. But one day, a version that is very different is likely to cross from birds or pigs, and be human-transmissible too, and (cue scary music) we could face something similar to the 1918 Spanish flu. Sign up for Sunday Brunch, the weekly Breakfast Bytes email.![]()
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