Influenza pandemics

Influenza pandemics can emerge unexpectedly and wreak global devastation. However, each of the six pandemics since 1889 emerged in the Northern Hemisphere following the flu season, suggesting that pandemic timing may be predictable. Fox and colleagues provide a possible explanation that seasonal flu epidemics may leave a wake of transient immunity in the population hindering pandemic emergence. Hypothetical seasonal flu epidemic spread (not based on real or simulated data) is depicted here with the colors indicating regions currently infected with seasonal flu (red), refractory and immune to pandemics (purple), and recovered and currently susceptible to a novel pandemic (blue). White lines depict the global flight network.
Image/Spencer J. Fox