The American media circus has moved on, the drugstores are removing the "H1N1 Vaccinations Available Here" signs, and most people are engaged with other concerns. Like SARS, avian flu and hantavirus, swine flu is yesterday's scare. But perhaps we're acting too fast in relegating this very real concern into the hall of fame for epidemics that might have been.
Our bout with swine flu killed more than 12,000 people in the U.S. alone, and more than 25,000 worldwide. Seasonal flu typically causes 36,000 deaths in the U.S. annually, but what's striking about H1N1 is that some 90 percent of its deaths occurred in people under 65.
At the influential Centers for Disease Control (CDC), they're hedging their bets. "The chances of a very large additional wave are very hard to predict," says Anne Schuchat, team H1N1 leader at the government agency. "We are not out of the woods."
But while the threat remains, swine flu lost its capacity for shock and awe after the disease peaked last October for reasons that are not completely clear. There was considerable fear that the number of cases would continue to climb through the winter, fostered by cold weather, low humidity and closed-in seasonal living.
In late March, confirming these fears at least in part, the CDC reported a spike of swine flu cases in the Southeast. The agency called the situation in Georgia, where 190 people were hospitalized from H1N1 virus over a three-week span, "critical."
And scientists are still studying pathways that could lead to a reappearance. A 2009 scientific paper by Japanese, Indonesian and American researchers concluded that non-virulent forms of avian H1N1 could yet combine with human strains to produce "highly pathogenic viruses."
Piecing Together the Pandemic
So what have we learned about swine flu? We'd know more if the origins of the virus were clearer, but much remains murky.
According to a National Academies (Institute of Medicine) workshop report on the 2009 outbreak, "This novel, swine-origin influenza A virus has now become the first pandemic of the 21st century." According to the report, the arrival of an influenza pandemic "was both anticipated and unexpected." It wasn't surprising that a readily transmissible virus would strike, but its appearance in the Americas rather than Asia "surprised many infectious disease experts."
But conditions were ripe, and the emergence of the flu just across U.S. borders meant it moved quickly, without the six weeks' lead time public health experts thought they'd have to prepare for strains from Asia. There is strong evidence that environmental factors—specifically, water pollution at a Smithfield Farms hog operation in Perote, Mexico—led to the outbreak last spring. The pork production plant there is one of the world's largest, slaughtering a million pigs annually, and local residents in Granjas Carroll (where 30 percent of the population were early victims of swine flu) complained that their water supply was contaminated.
Climate change has also been implicated in the spread of the virus. According to the Wildlife Conservation Society, new strains of avian flu were created when changing weather led to insect population explosions. The wild birds that eat those insects spread the disease to poultry, pigs and people—which was the case with avian flu in Asia. As Time magazine described it, "Pigs make particularly good biological mixing bowls since they can be infected by bird-, swine- and human-flu viruses and provide a hospitable environment for the viruses to swap genes and create entirely new strains in a process called reassortment."
This "reassortment" is what led scientists to worry that the virus could come back, stronger than before. "That's something we'll be paying special attention to," says Dick Thompson of the World Health Organization.
"Nearly 75 percent of emerging and re-emerging infectious diseases in recent years have been transmitted to people directly or indirectly from animals," says the New York State Department of Health. The animal connection is there also with virulent outbreaks of Ebola, West Nile virus, Lyme disease and SARS, and diseases are spread through easy air travel and population growth. Looking at the source of emerging pathogens, the NAS workshop said, "Almost every emerging disease (perhaps every single one) was driven to emerge by some type of change in human behavior or demography [population], or anthropogenic environmental change." In other words, they're not natural events, but are influenced by our mobility and proximity to wildlife.
A System on Overload
Looking at the H1N1 crisis and how it was handled, the Trust for America's Health points out, "Even with a mild outbreak, the health-care delivery system was overwhelmed" and "communication between the public health system and providers was not well coordinated."
The measures taken—shutting down schools, distributing masks and ordering zealous hand-washing—in hindsight appear to have been useful. Dr. John Santa of Consumer Reports called it "a public health success story." In fact, a 2007 review published by the Cochrane Collaboration concluded that the best preventative against flu spread is "hygienic measures around young children"—and washing hands is number one on the list.
Schoolchildren were heavily affected by the first wave of the 2009 outbreak. But many recovered and became immune, and school vacations also helped slow down the spread. A 1957-1958 virus outbreak in Louisiana affected 60 percent of schoolchildren in its first wave. So keeping kids home last year made sense.
Mixed with the good advice, however, was rumor and speculation. Considering that a great deal of misinformation quickly spread—leading to the boycotting of food products from Mexico, the quarantining of Mexican tourists in China, and the wholesale slaughter of pig populations in Egypt, even though the disease cannot be spread by eating pork—a good case is made for more global coordination and what the Wildlife Trust called the adoption of "policies internationally to encourage science-based, consistent decision-making across borders during an outbreak."
Since the outbreak, the Mexican government—criticized for a slow, uncoordinated response in the crisis—has invested $330 million in vaccination programs, laboratory equipment and other supplies. But it is unlikely that significant steps have been taken to reform Mexico's extensive and lucrative factory farms, which often (as in the case of Smithfield Farms) have absentee U.S. owners. If the virus started there, it could also be reborn there.
The causes of any viral spread are complex, and it would be easier to take lessons from the avoided epidemic if we knew exactly how we avoided it in the first place. Why did the disease form a wave that then receded? "I can't find anybody who can tell me a biological explanation that makes sense," says Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
One thing we do know: H1N1 isn't gone, just hiding. The virus, says the Washington Post, will "eventually infect—but not necessarily sicken—nearly everybody on earth who isn't already immune to it through vaccination. It may take years. It could happen by unpredictable waves or slow percolation. But it is virtually inevitable."
Jim Motavalli is an online contributor to the New York Times, CBS Interactive, Hearst and the Mother Nature Network. He is the author or editor of six books, including Forward Drive: The Race to Build Clean Cars for the Future.