  We study the spatio-temporal patterns of the proportion of influenza B out of
laboratory confirmations of both influenza A and B, with data from 139
countries and regions downloaded from the FluNet compiled by the World Health
Organization, from January 2006 to October 2015, excluding 2009. We restricted
our analysis to 34 countries that reported more than 2000 confirmations for
each of types A and B over the study period. We find that Pearson's correlation
is 0.669 between effective distance from Mexico and influenza B proportion
among the countries from January 2006 to October 2015. In the United States,
influenza B proportion in the pre-pandemic period (2003-2008) negatively
correlated with that in the post-pandemic era (2010-2015) at the regional
level. Our study limitations are the country-level variations in both
surveillance methods and testing policies. Influenza B proportion displayed
wide variations over the study period. Our findings suggest that even after
excluding 2009's data, the influenza pandemic still has an evident impact on
the relative burden of the two influenza types. Future studies could examine
whether there are other additional factors. This study has potential
implications in prioritizing public health control measures.
