Will the announced influenza pandemic really happen?
  We propose two simple probability models to compute the probability of an influenza pandemic. Under a random walk model the probability that all pandemics between times 0 and 300 occur by time 150 is 1/2. Under a Poisson model with mean inter arrival time of 30 years the probability that no pandemic occurs during at least 60 years is 14%. These probabilities are much higher than generally perceived. So yes the next influenza pandemic will happen but maybe much later than generally thought. 
Rinaldo B. Schinazi