Map created by CUHK SpatioEpi Group
Between the end of 2017 and the beginning of 2018, the influenza epidemic has occurred not only in Hong Kong but also the world. The map shows the distribution of main influenza subtype during this Winter influenza season of the northern hemisphere (between week 45 of 2017 and week 8 of 2018). These main reporting subtypes were confirmed in laboratory, and could be categorized as subtype A, B and C. Subtype A can be further classified as A (H1N1) and A(H3N2), etc., and subtype B as B (Yamagata lineage) and B (Victoria lineage), etc. Subtype C is however not common. It can be seen that the circulating subtype of a place is the same as that among countries nearby. For instance, the main subtype in China and her nearby south-east Asian countries is B, and the main subtype in North America (USA and Canada) is A(H3N2). From another perspective, there’s little relationship between the virus circulating in USA and Hong Kong or China.
The reported influenza subtype data on the maps were obtained from the WHO FluNet http://www.who.int/influenza/gisrs_laboratory/flunet/en/.
Influenza is a respiratory infection caused by the influenza virus, different forms of which are normally circulating in not just human beings but pigs and birds. All influenza viruses are divided into A, B and C, and further distinguished by their H and N antigens. There are currently 18 H (standing for haemagglutinin) and 11 N (standing for neuraminidase) antigens. Epidemics occurred when novel viruses are introduced to the human population. Pandemic influenza A (H1N1), previously referred as Swine flu, was an example causing worldwide outbreaks in 2009. The genetic structure of this influenza virus contains segments from pig, bird and human, reflecting the occurrence of reassortment. Studies suggested a case fatality rate of 0.4% for the novel infection, and a higher tendency for causing disease in young people compared to other forms of seasonal flu. Since 2009, the same virus has continued to cause outbreaks in different populations at different timepoints.