Since 1580, there have been 31 instances where new influenza viruses have emerged from their natural reservoir--wild aquatic birds--and through genetic reassortment in intermediary hosts such as pigs, have "jumped" to human populations with marked increases in human deaths. This change in ability to kill humans is related to a lack of any protective immunity and genetic factors of the virus. The end result in an increase in the number of deaths in healthy individuals between the ages of 18 and 30.
In the last century, the "Spanish flu" pandemic of 1918-1919 killed 50 million to 100 million people. Of those, about 500,000 were in the United States. Although the number of deaths is often noted as being between 20 million and 40 million, more recent critical analyses support the higher number.
The Asian flu pandemic in 1957 and the Hong Kong flu in 1968 each caused an estimated 2 million to 8 million deaths. Based on the current situation with avian influenza (a strain called H5N1) in Southeast Asia, influenza experts worldwide believe the conditions are "very ripe" for another pandemic to occur within the next several years. Although the bird strains of influenza virus have not yet genetically reassorted to result in human-to-human transmission of the virus, this is all that remains before another pandemic will occur.
To date, 43 human cases of H5N1 infection in Vietnam and Thailand have occurred as a result of direct exposure to infected birds; 28 have died. The patients have many similarities to the patient age and disease severity of the 1918-1919 pandemic. The projected number of deaths as a result of another influenza pandemic, based on the 1918 data, is more than 1.7 million in the United States over an 18-month period.
The most staggering figure from this estimate is that nearly 50 percent of those deaths will occur among people between the ages of 15 and 44. This segment of the population is typically considered to be the group that is least affected by influenza.
The World Health Organization estimates that between one-quarter and one-third of the world's population will become infected by an influenza pandemic, causing between 16 million and 21 million deaths worldwide. Recently, a senior WHO official in Southeast Asia indicated that between 30 million and 100 million people would die worldwide with the future pandemic.
When people hear projected death tolls in the millions from the influenza, many simply dismiss the predictions as far-fetched doomsday scenarios. In today's society, we tend to believe that modern medicine can conquer or control anything. Despite medical advances since the 1918 influenza pandemic, medical science is still unable to cope with the severe disease associated with influenza and many will die within 48 hours of the onset of the disease.
The 2004 flu vaccine shortage in the United States demonstrated the vulnerabilities in the vaccine production and distribution system. The public health and health-care delivery systems were unprepared, rationing was implemented and the public was disturbed by the shortages, providing only a snapshot of the situation and ensuing panic that could result from a larger epidemic.
Regardless of which risk model you use, an influenza pandemic will result in the biggest insurance loss ever--bigger than even the World Trade Center disaster. An extremely conservative estimate by the Centers for Disease Control and Prevention, using the lowest of estimates of pandemic-associated deaths, determined the overall economic impact to the United States at $71.3 billion to $166.5 billion, not including disruption to commerce and society.
It's hard not to get fixated on the numbers, especially when forecasting models that vary so widely. Theissue is that when a pandemic occurs, large numbers of people will be ill quickly.Many will need medical care and a hospital bed. A panicked population will be afraid to go outside, let alone to work or go overseas.
Global trade will slow to a standstill. In addition to direct health costs, indirect costs resulting from lost productivity when large numbers of workers are out sick or die will be significant. Replacing those lost permanently to the workforce will cause economic disruption and might add considerable costs to the overall national economic loss. Vaccination and antiviral drugs can reduce influenza morbidity and mortality, but their initial availability will be extremely limited. The large-scale production of a new pandemic vaccine, if even possible, will take several months.
Influenza experts from around the world warn that the international vaccine system is inadequate and that hospitals lack surge capacity. They believe pandemic preparedness efforts are moving too slowly and that governments and vaccine companies are dismissing the potential disaster as merely hypothetical. At the same time, the WHO is urging preparations for a pandemic as a matter of national security.
MICHAEL T. OSTERHOLM
is the director of the Center for Infectious Disease Research and Policy, associate director of the Department of Homeland Security's National Center for Food Protection and Defense and professor at the University of Minnesota'sSchool of Public Health.
ERIK RASMUSSEN is vice president of risk management for ING Re's Group Life, Accident and Health Reinsurance operation in Minneapolis.
April 15, 2005
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