Through a quantitative analysis of laboratory-confirmed weekly
type- and subtype-specific FluNet data from 19 countries, we
found both support for previously-held seasonal and type and
subtype dominance patterns  as well as novel patterns of
interhemispheric synchrony and latitudinal gradients in epidemic
timing. First, the type and subtype data confirmed the well-
established pattern of influenza epidemics occurring primarily
during the winter months in temperate regions. Additionally, H3
appeared to be the most dominant subtype, followed by type B and
then H1  . No significant differences were found between the
mean size of H1 and B epidemics; however, this outcome is most
likely from B epidemics being more frequent but typically
smaller than the H1 epidemics that did occur. Second, B
epidemics occurred later in the season than H3 and H1 epidemics
in the Northern Hemisphere, a pattern not previously described.
Third, we found that influenza B was at times codominant with
either H3 or H1, while these two subt