Avian Flu: How Scared Should We Be?

For the past two years, scientists, public-health officials and even a high-ranking government official or two have warned about the potential danger of a deadly worldwide outbreak, or pandemic, of avian flu. But it took a couple of furies named Katrina and Rita to really bring home how much can go wrong if you don't plan for major emergencies.

Suddenly old warnings about flu, which had seemed so remote, were sounding a lot scarier. The World Health Organization (WHO) declared in September, once again, that as far as an influenza pandemic is concerned, the question is not if but when, not whether millions would die but how many millions. President George W. Bush talked last week for the first time about how he, as Commander in Chief, might respond to an epidemic, raising the possibility of using troops to enforce quarantines. He also recommended that folks read John Barry's book on the 1918 pandemic that killed more than 50 million people worldwide and that serves as a reminder of the kind of threat that the world could face (see ESSAY). A reconstruction of the 1918 virus, reported in scientific journals last week, shows it to be an avian strain that mutated just enough to infect humans directly and easily.

The prospect of a flu epidemic makes us wobbly. We bounce back and forth between being scared silly and just plain apathetic. Influenza regularly kills 1 million people a year--36,000 of them in the U.S.--yet most of us don't get vaccinated. The new threat requires a different response--a healthy respect for the toll that even a moderate pandemic may take on our society and just enough genuine fear to figure out some smart steps to take to minimize the damage. "We need to scare people into their wits, not out of them," says Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. With that in mind, here's a primer on the risks of a flu epidemic and the government's preparations for countering it.

•HOW DOES A FLU THAT KILLS BIRDS BECOME A FLU THAT KILLS PEOPLE?

All influenza viruses--if you trace their lineage back far enough--got their start in birds, and the great majority stay there. But a handful of flu viruses adapt to the point that they can infect people. Each year the viruses capable of invading human cells mutate slightly in a way that leads to fresh outbreaks, but most people will still have a partial immunity because of previous exposure to similar viruses. Occasionally, though, a strain that had seemed to infect only birds will cross over more or less intact into humans. Because this new strain is so different from garden-variety flu viruses, few people are immune. That is apparently what happened in 1918 and in Hong Kong in 1997, then later in Vietnam and Thailand and in Indonesia this summer and fall.

Virologists named the newest strain of avian flu H5N1, after two proteins (hemagglutinin and neuraminidase) that dot the surface of the virus like spikes on a mace. Since 2003, more than 100 people have become sick enough to come to the attention of health authorities, and at least 60 of them have died. So far, the vast majority have been infected through close contact with birds; human-to-human infection is still extremely rare. What gives health authorities nightmares is the possibility that the lethal H5N1 could mutate into a virus that is easily passed among humans.