Regarding the mysterious biennial periodicity, I dug around for naturally occurring biennial events that have a synced timing. Didn’t find much, but I did find

Regarding the mysterious biennial periodicity, I dug around for naturally occurring biennial events that have a synced timing. Didn’t find much, but I did find this article specifically about biennial periodicity in measles. “Periodicity, synchronization and persistence in pre-vaccination measles” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4938089/#!po=0.769231 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4938089/#!po=0.... >An analysis of data from more than 350 administrative areas in England and Wales using wavelets [9] showed that for pre-vaccination measles, (from 1944 to 1966) most locations are indeed synchronized and present outbreaks every 2 years...