Seasonality and influenza virus strains for vaccines in the Asia-Pacific region

Abstract

The Asia-Pacific region spans a full range of climates, from northern temperate, through tropical, to southern temperate. Although influenza surveillance activity in this region is not complete, surveillance data that are available clearly demonstrate that the seasonality of influenza ranges from a typically winter disease in the temperate regions to a year-round infection in the tropical regions. Peaks of activity are observed in tropical regions; however, these are only now becoming better defined following the introduction and increased intensity of surveillance programmes. Similarly, the burden of disease associated with influenza activity, although clearly defined in temperate climates, is poorly defined in tropical countries. However, as more studies are conducted, the disease and mortality associated with increased influenza activity is increasingly demonstrated. In temperate climates where influenza seasonality is clear, World Health Organization (WHO) guidelines for vaccine strain composition follow either the February meeting for the northern hemisphere or the September meeting for the southern hemisphere. Currently in tropical countries, most influenza vaccination is carried out among travellers to the Middle East for religious festivals and to the northern hemisphere. Here, the most current northern hemisphere vaccine is the appropriate vaccine to use. As the burden of disease is clarified in tropical countries and the need for influenza vaccine clearly identified, the accurate definition of influenza seasonality in these countries will be required for the optimum timing of influenza vaccination programmes. Only then can clear recommendations be developed for the most current vaccine, which may be either the northern or southern hemisphere composition, in that specific country.