Bird flu (H5N1) has receded from international headlines for the moment, as few human cases of the deadly virus have been reported this year. But when Dutch researchers recently created an even more deadly strain of the virus in a laboratory for research purposes, they stirred grave concerns about what would happen if it escaped into the outside world. “Part of what makes H5N1 so deadly is that most people lack an immunity to it,” explains Marc Lipsitch , a professor of epidemiology at Harvard School of Public Health (HSPH) who studies the spread of infectious diseases. “If you make a strain that’s highly transmissible between humans, as the Dutch team did, it could be disastrous if it ever escaped the lab.”
H5N1 first made global news in early 1997 after claiming two dozen victims in Hong Kong. The virus normally occurs only in wild birds and farm-raised fowl, but in those isolated early cases, it made the leap from birds to humans. It then swept unimpeded through the bodies of its initial human victims, causing massive hemorrhages in the lungs and death in a matter of days. Fortunately, during the past 15 years, the virus has claimed only 400 victims worldwide—although the strain can jump species, it hasn’t had the ability to move easily from human to human, a critical limit to its spread.