Avian flu: The next pandemic?

November 7, 2005

The next big battle the world faces may be against the tiniest of terrorists: the avian flu virus. Some experts predict it is only a matter of time before an avian flu virus becomes readily transmissible between humans. Once that happens, an avian flu pandemic could affect nearly every country in the world.

"The next pandemic is likely to be caused by a mutant of the virus [H5N1] that is causing the bird flu in Asia," said David Nabarro, M.D. Nabarro was selected by the United Nations in September to coordinate the battle against avian flu.

"It is notif it is going to happen but when, where, and how bad," Michael Osterholm, M.D., ventured at a meeting sponsored by the Woodrow Wilson International Center for Scholars' new Global Health Initiative. He is director of the Center for Infectious Disease Research & Policy and associate director of the Department of Homeland Security's National Center for Food Protection & Defense.

Both Sanofi-Aventis and Chiron Corp. have grants from the National Institutes of Health for avian flu vaccine research. First results of Sanofi-Aventis' human trials were favorable, and the Department of Health & Human Services awarded the company a $100 million contract to produce enough doses to treat the highest-risk people. Sanofi-Aventis would then be given the green light to produce more vaccine.

At the end of September, the Senate added just under $4 billion to the defense spending bill, earmarked for this potential emergency. Most of the money would go to purchasing antiviral drugs and vaccines.

HHS intends to stockpile approximately 20 million doses of the antiviral drug oseltamivir (Tamiflu, Roche). While that's not nearly enough, Roche has agreed to negotiate with generic drug manufacturers to increase Tamiflu production. Mylan Laboratories, among other firms, are prepared to produce oseltamivir to fill this public health need.

A newly published Centers for Disease Control & Prevention study suggests that having antivirals on hand to treat 20%-25% of Americans would be enough to treat most cases and reduce hospitalizations. But 20 million doses for a population of 300 million falls short. And it's nowhere near the goal of 150 million that Senate Majority Leader Bill Frist (R, Tenn.) would like to see.

A limited arsenal

While experts believe Sanofi-Aventis' H5N1 vaccine is now the most effective drug to prevent infection, an outbreak could occur with a variant virus. The variant would require a new vaccine, which could again take months.

For treating people once they are infected, we are left with antivirals. "Resistance to amantadine and rimantadine, two older antivirals, has already been shown," said Jeffery A. Goad, Pharm.D., MPH, FCPhA, FCSHP, assistant professor of clinical pharmacy at the University of Southern California. Goad specializes in infectious diseases and immunizations.

The neuraminidase inhibitors, oseltamivir and zanamivir (Relenza, GlaxoSmithKline), are two newer antivirals that appear to be somewhat effective in reducing the severity and preventing the transmission of flu viruses, including H5N1. However, treatment with either of these drugs must begin within 48 hours of symptom onset. And H5N1 infections, Goad said, might require higher doses and longer durations.