Influenza Pandemic
According to the World Health Organization, an influenza pandemic occurs when a new influenza virus appears against which the human population has no immunity, resulting in several, simultaneous epidemics worldwide with enormous numbers of deaths and illness. With the increase in global transport and communications, as well as urbanization and overcrowded conditions, epidemics due the new influenza virus are likely to quickly take hold around the world.
A new influenza virus: how it could cause a pandemic
Annual outbreaks of influenza are due to minor changes in the surface proteins of the viruses that enable the viruses to evade the immunity humans have developed after previous infections with the viruses or in response to vaccinations. When a major change in either one or both of their surface proteins occurs spontaneously, no one will have partial or full immunity against infection because it is a completely new virus. If this new virus also has the capacity to spread from person-to-person, then a pandemic will occur.
Outbreaks of influenza in animals, especially when happening simultaneously with annual outbreaks in humans, increase the chances of a pandemic, through the merging of animal and human influenza viruses. During the last few years, the world has faced several threats with pandemic potential, making the occurrence of the next pandemic just a matter of time.
Consequences of an influenza pandemic
In the past, new strains have generated pandemics causing high death rates and great social disruption. In the 20th century, the greatest influenza pandemic occurred in 1918 -1919 and caused an estimated 40–50 million deaths world wide. Although health care has improved in the last decades, epidemiological models from the Centers for Disease Control and Prevention, Atlanta, USA project that today a pandemic is likely to result in 2 to 7.4 million deaths globally. In high income countries alone, accounting for 15% of the worlds population, models project a demand for 134–233 million outpatient visits and 1.5–5.2 million hospital admissions. However, the impact of the next pandemic is likely to be the greatest in low income countries because of different population characteristics and the already strained health care resources.
If an influenza pandemic appears, we could expect the following:
Detecting a new pandemic virus
Continuous global surveillance of influenza is key. WHO has a network of 112 National Influenza Centres that monitors influenza activity and isolates influenza viruses in all continents. National Influenza Centres will report the emergence of an “unusual” influenza virus immediately to the WHO Global Influenza Programme or to 1 of the 4 WHO Collaborating Centres. Rapid detection of unusual influenza outbreaks, isolation of possible pandemic viruses and immediate alert to the WHO system by national authorities is decisive for mounting a timely and efficient response to pandemics.
Preparing for an influenza pandemic
Contingency planning for an event sometime in the future is often difficult to justify, particularly in the face of limited resources and more urgent problems and priorities. However, there are two main reasons to invest in pandemic preparedness:
1. Preparation will mitigate the direct medical and economic effects of a pandemic, by ensuring that adequate measures will be taken and implemented before the pandemic occurs.
2. Preparing for the next influenza pandemic will provide benefits now, as improvements in infrastructure can have immediate and lasting benefits, and can also mitigate the effect of other epidemics or infectious disease threats.
For more information and preparedness checklists: http://pandemicflu.gov/plan/checklists.html
Avian Influenza Fact sheet: http://www.who.int/csr/don/2004_01_15/en/