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Originally Posted by W.F. Tomba
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Originally Posted by beskeptical
When an infectious disease works its way through a population some immunity is conferred. As the population is replaced by new and therefore not previously infected members, the potential for a new epidemic increases each year. With some diseases such as measles, (before vaccines), which does not mutate as readily as flu virus, local epidemics used to occur every 3-5 years. That's how long it took to add enough susceptible members to allow sustained transmission of virus.
With other diseases, these patterns are complicated by the organisms own cycle. As flu virus mutates, there is a potential for deadly combinations of its genetic components. Just as with a coin toss, it may not be predictable which side will face up with each toss, but it is predictable over time you will eventually get the other side.
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I accept what you say about the cyclical behavior of epidemics, but do we know of a cyclical process for virus mutations? Or do we have evidence that there is one? Even if we don't, it's prudent to consider that there might be one, since cyclical processes are so common in biology. I'm just saying that it's not a given.
As for the coin toss, what you say is true, but note that the number of tosses that have elapsed since you last got heads has no bearing on your chances of getting heads over any future series of tosses. Because there is no cyclical mechanism behind coin tosses, you can never be overdue for heads. ( Gambler's Fallacy)
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If you tossed that coin for a sufficient amount of time, you could collect reasonable data of the average time between getting the opposite side and the longest time one has ever gone only getting one side. For gambling and pure random coin tossing, each coin toss has a new 50:50 chance of landing on one side. But for biological systems the range and averages do rely on more than chance. You can often find the patterns before understanding the underlying mechanisms.
Some suggested mechanisms would be the life cycle of flu virus pandemics is such that it not only includes time for the susceptible population of humans to regenerate, but that there is also a pattern in wild birds and domestic poultry interacting with the human outbreaks. These cyclic avian outbreaks occur when they cross the species barrier. So the new viruses have to emerge first in the poultry, spread to ducks, then to pigs then to humans. Each new cycle takes x number of years on average with a range of y years. Once the virus emerges it is more pathogenic until milder versions are naturally selected. (Kills too fast, dies out, host survives, virus passed on.) The range of lethality could be from mild to severe. Any single new pandemic could cause mild or severe disease but the regularity of the pandemics could be very predictable.
What we have now is a pandemic overdue. The lethality might be unknown with each new pandemic but all signs are a doozy is forming.