Table 1.

Key findings of molecular and epidemiological studies describing the spatial transmission dynamics of the 2009 influenza A/H1N1 pandemic.

pandemic period	epidemiological studies	molecular studies
early pandemic stage (Jan–July 2009):	— first cases in an outbreak in the community of La Gloria, Mexico: 15 February 2009 [28] — little community transmission; multiple introductions — few locations experience spring wave (greater Mexico City area, some US cities, London) [29] — temperate Southern Hemisphere and tropical locations in Asia and Latin America experience summer waves — Closing schools early in the pandemic reduces transmission by 30–50%	— most likely time of origin in Mexico: January–February 2009 [28,31] — dissemination from Mexico to the USA during February to April [32] — spread from the USA to Europe and Asia [32] — spring wave in the USA: strong spatial structure and co-circulating lineages in the USA [33] — summer wave in Scotland: a major lineage originated in UK and other multiple introductions from both international and UK sites [34] — low level of on-site transmission and intensive spatial mixing within an individual community in San Diego [35]
late stage (Aug–Dec 2009):	— slow spread of the autumn wave in the USA driven by distance; little impact of school closures [30] — great diversity in number, timing, and intensity of pandemic waves between and within countries [30]	— autumn wave in the USA: less spatial structure; single lineage-dominated [33] — single lineage-dominated worldwide in autumn [33] — winter wave in Scotland: more diverse genetically with several clades of similar sizes in different locations; extensive mixing [34]