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The American Experience

Flu Trackers

Those learning for the first time of the devastating consequences of the worldwide 1918 influenza pandemic typically respond with two questions: How could they have never heard of a world-wide scourge that killed upwards of 30 million people? And, could it happen again?

Addressing the first question, journalist H.L. Mencken, offered this theory in 1956: "The epidemic is seldom mentioned, and most Americans have apparently forgotten it. This is not surprising. The human mind always tries to expunge the untolerable from memory, just as it tries to conceal it while current." Others point to an international pre-occupation with World War I and its outcome as obliterating all competing concerns. Finally, some speculate that the 1918 flu hit with such deadly force and over such a relatively short period of time that clear-eyed historical perspective was not possible.

Lung Tissue from 1918 influenza victim. Confronted with the question of whether such an event could happen again, modern virologists respond with a sobering, "Yes." To comprehend how this is possible, it is necessary to understand how influenza viruses are passed from species to species, and what makes one treatable and another deadly.

Generally, birds, pigs, and humans are the principle players in a viral chain reaction that determines how serious an influenza outbreak is going to be. As viruses are exchanged between various members of various species, subtle changes to the viruses' genetic material can occur. Usually such mutations are minor, resulting in a process called antigen drift. Even minor changes in the virus's make-up, however, mean that new vaccines must be developed to combat it. When significant mutations occur antigen shift results. An example of antigen shift is seen when a flu virus from a bird and a flu virus from a human combine inside a pig and result in a new, virulent strain. Scientists speculate that such a scenario sets the scene for pandemics such as those of 1957 (the Asian flu, which killed 70,000 Americans) and 1968 (the Hong Kong flu, which resulted in the deaths of 28,000 Americans) and point out that incidents of antigen shift resulting in pandemics occur roughly every 30 years. By that calculation, an influenza pandemic could be expected in the near future.

The responsibility of tracking emerging influenzas and predicting which ones pose a serious threat to human populations falls to several government health agencies: the Centers for Disease Control and Prevention (CDC), the National Institutes of Health (NIH), and the Food and Drug Administration (FDA). These US agencies combine forces with the World Health Organization (WHO) and attempt the tricky task of flu forecasting. An international surveillance network of flu trackers records and disburses data regarding outbreaks, in various species, from all over the globe.

In recent years, new flu strains have been seen originating in Asia with some regularity. Health authorities believe the close proximity of people, birds, and pigs found in Asian nations contributes heavily to influenza virus propagation. Information gathered by modern flu trackers is used to develop each year's flu vaccine, which is given to millions of people the world over. However, the composition of the vaccine itself is, to some degree, the product of scientific guesswork. In order for drug companies to have flu shots ready for the annual autumn inoculation period, they need to start making them by late winter. To do this they must rely on forecasts, based on the previous winter's flu activity, as to which strains are more likely to pose a threat in the coming flu season. Quite often the forecasts are correct and the vaccines are effective; only 1% of people in the US who contract the flu are hospitalized. Additionally, doctors have at their disposal a vast array of antibiotics with which to treat secondary illnesses, such as pneumonia, that strike many flu victims. There are instances, however, where an unforeseen influenza strain will cause an alarm to be sounded at the height of flu season.

In May 1997, influenza-watchers once again turned their attention to Hong Kong, where doctors were trying to determine if an avian (bird) virus that infected and killed a three-year-old boy could be passed from person to person. By late December of that year, millions of chickens in Hong Kong had been ordered destroyed as more cases of avian viruses in humans were reported. The prospect of such an influenza virus spreading through human populations was considered particularly alarming because humans carry no natural immunity to avian virus. A vaccine, if one could be developed at all, would take months to test and distribute. And because influenza vaccines are usually grown within chicken eggs to begin with (and this strain of virus kills chickens), scientists would be faced with the task of engineering a form of the virus that does not kill the chicken eggs.

A number of public health experts believe that as global travel expands, cases of "rogue" influenza outbreaks may become more common. The world's underdeveloped areas, where overpopulation and poor sanitation often abound, are increasingly visited by travelers from urban centers who return home carrying more than just their passports. The very speed and frequency of modern travel could, therefore, work against public health authorities racing to control a pandemic.




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