Influenza virus strains identified during epidemics in South America may frequently become predominant in later epidemics in Central and North America, according to recent findings.

From 2002 to 2013, South America reported 877,770 respiratory samples positive for influenza (2.8 per 10,000 persons annually) and North America reported 4,535,508 cases (9 per 10,000 persons annually). From 2006 to 2013, Central America reported 82,163 results (2.4 per 10,000 persons annually).

Although epidemic influenza B virus strains in South America later predominated in 50% of seasons in Central America and 55% of subsequent North American seasons, the North American incidence increased to 73% after accounting for all identified virus strains, rather than only those that predominated in South America.