The World Health Organization ( WHO) convenes technical consultations in February and September each year to recommend viruses for inclusion in influenza vaccines for the northern and southern hemisphere influenza seasons, respectively.

This recommendation relates to the influenza vaccines for use in the forthcoming northern hemisphere 2018-2019 influenza season. A recommendation will be made in September 2018 relating to vaccines that will be used for the southern hemisphere 2019 influenza season.For countries in tropical and subtropical regions, WHO recommendations on influenza vaccine composition (northern hemisphere or southern hemisphere) are available on the WHO Global Influenza Programme website.Between September 2017 and January 2018, influenza activity was reported in all regions, with influenza A(H1N1), A(H3N2) and influenza B viruses co-circulating. 

In the temperate countries of the southern hemisphere, influenza activity remained high until October. In temperate South America, activity remained above seasonal threshold until October with influenza B viruses predominating.In Oceania, seasonal activity continued until late October with cocirculation of influenza A(H3N2) and B viruses. In southern Africa there was regional activity with predominantly influenza B viruses until October.In the temperate countries of the northern hemisphere, influenza activity started early in North America from November with predominantly influenza A(H3N2) viruses. There were very high levels of influenza-like illness (ILI), hospitalizations and mortality due to influenza in the United States of America compared to recent seasons. 

Influenza activity in Europe started in December in the south and west followed by the north and east. Influenza B viruses (Yamagata lineage) predominated followed by influenza A viruses. The dominant subtype of influenza A viruses varied depending on the country.The majority of countries reported ILI reaching moderate levels in comparison with recent years, with few countries reaching levels exceeding those of recent years. Some countries reported levels of hospitalization and intensive care unit admissions reaching or exceeding peak levels of recent influenza seasons. 

In East Asia, influenza activity started to increase from December with influenza A(H1N1)pdm09 and B (Yamagata lineage) viruses with the exception of the Republic of Korea which had predominantly influenza A(H3N2) and B viruses. ILI activity in China (northern and southern) and Japan reached levels higher than recent influenza seasons. In western Asia, influenza activity started to increase from October with predominantly influenza A(H1N1)pdm09 viruses.