Influenza causes seasonal outbreaks each year and periodically causes a pandemic. The World Health Organization (WHO) Global Influenza Surveillance and Response System (GISRS) has contributed to global understanding of influenza patterns, but limited regional analysis has occurred. This study describes the virological patterns and influenza surveillance systems in the 11 countries of the WHO South-East Asia Region.

Virological data were extracted in January 2018 from FluNet, GISRS's web-based reporting tool, for 10 of the 11 countries that had data available for the years 2009 to 2017. Descriptive data for 2017 on influenza surveillance systems, including the number of sentinel sites, case definitions and reporting frequency, were collected through an annual questionnaire.

Data on surveillance systems were available for all 11 Member States, and 10 countries reported virological data to FluNet between 2009 and 2017. Influenza surveillance in the region and national participation increased over the 8 years. Seasons varied between countries, with some experiencing two peak seasons and others having one main predominant season. Bangladesh, Indonesia and Myanmar have only one season: Bangladesh and Myanmar have a mid-year pattern and Indonesia an end-year pattern. Influenza A was the predominant circulating type for all years except 2012 and 2016, when A and B co-circulated. Influenza A(H1N1)pdm09 was dominant in 2009 and 2010 (77% and 76%, respectively), 2015 (72%) and 2017 (54%); influenza A(H3) accounted for approximately half of the positive specimens in 2011 (46%), 2013 (51%) and 2014 (47%); and influenza B (lineage not determined) made up over 49% of positive specimens in 2012.

Although the timings of peaks varied from country to country, the viruses circulating within the region were similar. Influenza surveillance remains a challenge in the region. However, timely reporting and regional sharing of information about influenza may help countries that have later peaks to allow them to prepare for the potential severity and burden associated with prevailing strains.