Comment Re:worry in october, not now (Score 1) 695
This is related to the idea of herd immunity -- that a population is essentially immune if the number of immune people is above some certain threshold. Think of it this way: if 90% of people are immune to a disease, and a person on average spreads this disease to 10 people, the transmission rate will be linear. If you pass below a threshold of, for example 80% though, it will become rapidly exponential.
After 68 years, the average turnover time of a generation, the numerator of immune people ends up decreasing, and this is why we get these cyclic pandemics.
While everyone knows about the H1N1 Spanish Flu (the same subtype as this new Mexican flu) of 1919, much fewer know about the 1978 pandemic of the same type. This is what we should be thinking about.
So, one might think, well, 68 years + 1978 = 2046. This pandemic is way too early. The problem is, however, that the 1978 pandemic was extremely mild -- it itself struck about 10 years too early. Thus, not many people were infected, leaving the numerator much smaller than it should be.
The other problem is the population explosion, especially in third world countries. This has the effect of drastically increasing the denominator of that herd immunity ratio.
Because of these two reasons, I suspect that the herd immunity ratio has already passed below the threshold needed to protect us from a pandemic.