3.1 Tracking the emergence of new strains
Influenza is one of several diseases monitored by the WHO(GAR) network (WHO, 2011a), comprising 110 ‘sentinel’ laboratories in 82 countries. The organisation’s surveillance and monitoring of the disease then forms part of their Global Influenza Programme (GIP), and they use data gathered from participating countries to:
- provide countries, areas and territories with information about influenza transmission in other parts of the world to allow national policy makers to better prepare for upcoming seasons
- provide data for decision making regarding recommendations for vaccination and treatment
- describe critical features of influenza epidemiology including risk groups, transmission characteristics, and impact
- monitor global trends in influenza transmission
- inform the selection of influenza strains for vaccine production (WHO, 2011b).
The influenza data from the sentinel laboratories is fed into a global surveillance programme, started by the WHO in 1996, called FluNet (WHO, 2011c), which is one of the tools that facilitates the actions described above.
Activity 1 Using FluNet
Use the link below to visit the WHO’s FluNet web page and locate and view the chart showing the global circulation of flu (in the section marked ‘View charts’) to find out which flu subtypes are currently the major ones in circulation in the human population.
At the time of writing (2011), Influenza A (H5N1) and influenza B (unknown lineage) are the two main types globally. FluNet also breaks this information down into geographic areas and countries so, if you wish, you can see what subtypes are circulating where you live.
Typically a flu vaccine contains material from the main influenza A strains and an influenza B strain, so that an immune response is induced against the most likely infections. Usually the scientists predict correctly and immunised people are effectively protected against the current strains (>90% protection). However, the prediction is occasionally incorrect, or a new strain develops during the time that the vaccine is being manufactured. In this case the vaccine generally provides poor protection.
What can you deduce about immunity against flu infection from the observations on vaccination above?
The immune response is strain-specific. If you are immunised against the wrong strain of flu, then the response is much less effective and you are more likely to contract the disease.