Patients crowd an emergency hospital near Fort Riley, Kan., in 1918. The… (Associated Press )
"THE threat of an influenza pandemic is, at present, one of the most significant public health issues our nation and world faces." — Dr. Andrew C. von Eschenback, commissioner of the U.S. Food and Drug Administration, April 2007
"We know that a pandemic will eventually occur. We always say it's not a question of if; it's a question of when." — Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention, April 2007
A year ago, concerns about pandemic flu were running high, with the threat of an outbreak making newspaper headlines and television newscasts. Now the specter of this threat has largely faded from the public mind — as if the risk has passed. But public health experts remain as concerned as ever about the possibility of an outbreak.
"We can't predict when an influenza pandemic will occur or which virus will cause it," says Nancy Cox, director of the influenza division at the CDC. "However, we can be almost 100% certain that there will be one."
It's that kind of conviction that's prompting public health experts to encourage people to prepare for an outbreak. Complacency needs to be replaced with knowledge and action.
Flu pandemics are caused by influenza A virus — the same virus responsible for the seasonal flus we suffer each winter. There's a reason we can catch flu again and again: Many different strains of the virus exist, and new forms are always emerging.
The virus is constantly undergoing subtle changes, called mutations, in its genetic material. These small changes are what make the seasonal flu viruses slightly different every winter and why a new flu immunization is required each year.
Occasionally, the virus undergoes a dramatic shift and a truly novel viral strain is created — one with pandemic potential. Because there is little or no immunity to the new form of the virus, it spreads easily and rapidly from person to person, and its global spread is considered inevitable.
Unfortunately, it is currently impossible to predict when a pandemic will break out and which viral strain will cause it. "The influenza virus is highly unpredictable," Cox says. It is also difficult to anticipate the magnitude of the outbreak. Experts estimate that a pandemic of relatively low severity could potentially cause 90,000 U.S. deaths if appropriate interventions are not made; in the case of a very severe pandemic, this number increases dramatically — to more than 1.8 million.
Currently, the virus of greatest concern is one found in wild birds that scientists refer to as "highly pathogenic avian influenza H5N1." More commonly known as "bird flu," the H5N1 virus has caused numerous outbreaks of disease around the world in domesticated birds such as chickens and turkeys and has proven to be highly lethal to them.
It can also be highly lethal to people. Although human infections with the H5N1 virus are rare, cases have been reported on several continents, including Asia, Africa and Europe. Most infections in humans have resulted from direct contact with infected birds and, so far, the virus appears unable to spread effectively from person to person.
The concern, however, is that the H5N1 virus will continue to evolve and eventually develop the capability for direct human spread. Should that occur, the stage is set for a widespread pandemic.
H5N1 bird flu is not the only virus experts are worried about. "The next pandemic virus could equally be an influenza virus of another subtype," Cox says.
Unfortunately, without knowing exactly which virus will trigger an outbreak, scientists cannot develop an effective vaccine. They can only do so after the pandemic strain emerges and is identified.
The government is not waiting for that to happen to start to prepare: Many agencies are ramping up pandemic plans. The Department of Health and Human Services has amassed enormous stockpiles of antiviral medications, including Tamiflu. To date, it has purchased 26 million antiviral treatment courses and expects to have 81 million available by the end of 2008 — enough to treat 25% of the U.S. population.
Earlier this year, the Food and Drug Administration approved a "pre-pandemic" vaccine targeting the H5N1 virus. The vaccine is based on current lethal strains of the virus, and experts believe that it may provide early, limited protection in the event of a pandemic. The entire supply of vaccine has been purchased by the federal government and will be stockpiled and distributed if the need arises.
Local agencies are also gearing up. Just last week, Los Angeles County's director of public health, Jonathan Fielding, unveiled an educational DVD for use in schools to help prevent students from catching seasonal flu and prepare them for a pandemic flu. It teaches kids simple steps to avoid the spread of flu, such as washing their hands often, covering their nose and mouth when they cough or sneeze, and avoiding touching their eyes, nose or mouth.