Now this is utter speculation on my part and I am no immunologist, virologist, epidemiologist, doctor, butcher, baker or even a candlestick maker. And I have not read anything in the science oriented popular press in regards to this speculation so I assume there is some glaring flaw to the hypothesis. But maybe if I voice this speculation, someone will set me straight on the flaw.
I am thinking about how other flu viruses which have caused pandemics have had a mild initial wave in the spring and then caused a more lethal wave in the fall when flu season starts up again in earnest. I can see how an emerging virus can become a faster spreading disease by simple selective pressure especially given how fast influenza viruses mutate and recombine. But what would lead a virus to become more dangerous over time? That would not seem to convey any particular advantage – it could happen by chance but there would be no reason to specifically predict that a flu virus would be more lethal in the next season. And yet it seems to have happened just this way with the 1918 and at least one of the other lesser pandemics if I recall correctly.
The cytokine storm view seems to explain the eventual lethality of the virus and why it is more likely to kill those with a health immune system but why does this happen in the second wave rather than the first? So here is the speculation: Most of the people who have a cytokine storm reaction might have been among those who were previously exposed. In the first, mild wave of the pandemic, they get the virus, mount an immune response and form immune memory cells for rapid reaction if the virus ever comes back. Because the initial immune response is slow, a cytokine storm is not triggered before the virus is cleared. Symptoms of the viral infection may go undetected. When the flu comes back into previously covered territory some of these folk who no longer have the antibodies in high concentrations but have the memory cells have their immune systems overreact.
That’s a long way of saying that it is possible, that like an allergy, a cytokine storm requires (or is more likely following) a primary exposure that does not provoke symptoms.
Maybe if I was more educated on cytokine storms I would not consider this a possibility. Unless someone sets me straight I can really do nothing but wait and see what happens in the fall. Probably nothing. But keep washing your hands – you may already have been exposed once!!!!1!!
UPDATE: An off-line chum of mine who wishes to remain anonymous asked someone with some background in the field and was told that it was an interesting question (thank you) but there are two issues. Firstly, we don’t have samples of the virus from each time period, only the more deadly one. So we can not know how similar or different they are. And secondly, there has been some research to suggest that people who were exposed the first time displayed some level of immunity during the second wave. Again, there is not a lot of hard evidence but what there is would be compatible with what one would expect without considering the first and second exposure scenario for cytokine storm susceptibility. So why the later waves of flu outbreaks like 1918 flu were more lethal is still up in the air. Bad luck? Some non-obvious selective pressure towards greater lethality? Unknown. Maybe the fall flu season won’t be more lethal. If it is, at least genetic sequencing might tell us why.