This is more likely the result of the widespread use of contraceptives.
Beginning in the 1960s, the Japanese used more condoms per capita than any other nation in the world.
Most pandemics occur when a pathogen jumps a species barrier to a new host (humans) that are not adapted to it. Such a process should be random and follow a Poisson distribution. The expected time between pandemics should therefore follow an exponential distribution. I am skeptical of the validity of a cyclical model predicting a definitive pandemic date.