Unprepared for a Pandemic

SOUNDING THE ALARM, AGAIN

More than a year and a half ago, Foreign Affairs published three articles that sounded a clarion call to prepare for the next pandemic. They warned that another pandemic could occur at any time and at a staggering cost to human health and the world economy. These facts remain incontrovertible. At the time, many public health scientists believed that recent outbreaks of the H5N1 influenza virus in birds in Asia, Europe, and Africa, with occasional infections in humans, were precursors to the next pandemic. They still do today.

Like earthquakes, hurricanes, and tsunamis, influenza pandemics are recurring natural disasters. The natural reservoir of influenza virus is wild aquatic birds. But for a human influenza pandemic to occur, a strain of an avian influenza virus must develop to which humans have no preexisting immunity and undergo critical genetic changes that allow it to be readily transmitted from person to person. The H5N1 strain of the influenza virus has had a limited impact on human health so far, but a human influenza pandemic could occur -- and be devastating -- if a current strain underwent the right genetic changes.

For decades, scientists believed that the only way for an avian influenza virus to become transmittable between humans was through a process known as reassortment. Reassortment occurs when an avian virus and a human virus both infect the same cells of an animal (a pig, for example) or a person and swap genes, creating a new virus adapted to humans. (This is how the 1957 and 1968 influenza pandemics began.) Over the past two years, however, studies of tissue samples from 1918-19 influenza victims have suggested that an influenza virus can also become a pandemic strain after undergoing genetic mutations of its own. Recent studies of the virus' genetic material have demonstrated that the 1918-19 virus likely evolved by a process known as adaptation, a series of critical mutations that rendered it capable of being transmitted between humans.

Although it is impossible to know for sure whether H5N1 will ever evolve into the next human pandemic virus, more and more of the genetic changes documented in the 1918-19 virus have also been found to have occurred in recent H5N1 strains affecting both birds and people. Meanwhile, the spread of H5N1 infections to more avian species and to more humans continues to point to H5N1 as a likely strain of the next pandemic.

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