Avian Flu: Pandemic Potential
Few people remember the devastating outbreak of influenza in 1918 and 1919, which killed an estimated 40 million people worldwide. Today, a new, potentially devastating strain of influenza — avian flu — is raising alarm in the public health community. David Ozonoff, a School of Public Health professor and chairman of the department of environmental health, conducts research on community health effects of toxic exposures, especially from hazardous waste sites, and new mathematical approaches to understanding the results of small case-control studies. He has a special interest in avian influenza and its pandemic potential. He talks about what the public health community should be doing to prepare for a possible pandemic.
Public health officials seem alarmed about a potential avian flu pandemic. What is avian flu, and why does it have pandemic potential?
First of all, avian flu is a type of influenza, a viral respiratory disease that typically peaks in the winter months in the northern hemisphere and causes familiar symptoms: typically sudden onset with fever, headache, and pain when moving the eyes, prominent muscle and joint aches, and a rapidly developing dry, hacking cough. Usually people get over the acute symptoms in four or five days, but they may continue to cough for weeks and feel tired and weak for months afterward. It is not only responsible for high absenteeism during the so-called flu season — November to March — but it is one of the most frequent reasons for seeking medical care. Because it’s caused by a virus, antibiotics aren’t effective, although they are frequently and inappropriately prescribed. That’s the typical picture. But a significant number of people, especially those who are older or very young, or those with other chronic health problems, get seriously ill and die.
Influenza and its complications are the direct cause of 36,000 deaths each year in the United States, more during a really bad season. And every 30 or 40 years, the virus develops pandemic potential — that is, it sweeps the globe, causing especially serious disease. This is what happened during the 1918â€“1919 pandemic, known as the Spanish flu, that killed an estimated 40 million people worldwide and hundreds of thousands in this country.
How does influenza turn into a pandemic virus?
This is a complicated question, but one thing to know about influenza is that it changes structurally from year to year, and so the general population has only partial immunity to new strains. We develop new flu vaccines each year to fight these new strains. A pandemic virus happens when the virus changes so much that our immune systems can’t recognize it or mount any kind of initial response. When a pandemic virus appears, almost no one has immunity. Hence, there is great potential for a worldwide epidemic, which is what a pandemic is.
So what has been observed so far about the avian flu?
The current virus that affects birds, especially poultry in Southeast Asia and China, is adapted to live in birds, not humans. It is very lethal to domestic poultry like chickens and turkeys, killing almost 100 percent of those infected, but bird viruses don’t usually attack humans. At least that was what we believed until 1997, when a small outbreak occurred in Hong Kong, although the origin of the virus was probably southern China. In fact, all previous pandemics likely started in this part of the world, because traditional ways of living often put people, pigs, and poultry close together in small hamlets and villages. Pigs can harbor both human and bird influenza viruses and thus become a type of mixing vessel for both types, and they may mix and match genetic material to produce new hybrids that have characteristics of each. Thus a virus that is mainly human but has some bird or pig characteristics would look very different to our immune systems. That’s probably the main way pandemic viruses get going.
What is unusual about the current outbreak of bird flu in Asia is that the virus jumped directly to humans from chickens without the pig intermediary as in the past. It is of a subtype that has not caused a human epidemic before, so we have no immune protection. And it has already accomplished two things necessary for a pandemic: it has jumped to humans and it causes serious disease. What it has yet to do convincingly is spread easily from person to person as ordinary flu does. There is sound evidence that the virus is mutating to pick up that ability as well. And when it does, it will spread around the globe in a few months. It moves quickly in migratory water fowl, and there is no way to contain it to Asia.
Aren’t scientists developing an avian flu vaccine?
There currently is no vaccine we know that is effective for this type of influenza, and we can’t easily make one until we know the exact strain of bird flu that will be involved in an epidemic. When we find that out, the vaccine production cycle is about six months, although strenuous efforts are being made to shorten that through cell culture methods. If a pandemic happens in the next year or two, we will be without a specific vaccine. A less specific H5N1 vaccine that may (or may not) provide some protection is only in the initial testing stages.
Aren’t there antiviral drugs to take once the flu hits?
There is an antiviral drug, Tamiflu, manufactured by Roche Pharmaceuticals, a Swiss company. Tamiflu must be given at very early onset of the disease or prophylactically to be effective. But it is in short supply, and other countries have put in orders ahead of the United States. The United States has only 2.1 million doses, and the drug has a 12-month production cycle. So if a pandemic happens in the next six months — which is quite possible, even thought likely by some — very few people in this country will get this drug.
What would be the consequences of a pandemic?
No one can say for sure, but it would put severe stress on virtually all of our society’s systems: not just medical care — for which the reserve capacity is slight or nonexistent — but also on all of our critical infrastructure, like food supply, civil safety, transportation, and anything else that would be affected by an absenteeism rate of up to 30 percent. There would be a drastic curtailment of trade and commerce. We live in a highly interdependent world where everything is done “just in time.” This means that when one system is severely crippled, say because truckers are reduced in number by a third or more, it ripples through the entire system.
That sounds dire. What should the world be doing to prevent or prepare for this?
In some ways, we are no better prepared to deal with a pandemic than we were 87 years ago. There is an on-paper plan to rush antiviral drugs to an affected area should an outbreak occur in Asia. But not many people think this will work. The places where this is likely to ignite have rudimentary public health systems. If a pandemic holds off for the next two years, we could ramp up antiviral production and vaccine technology. But equally important is trying to improve the public health infrastructure, even in this country. If we had vaccine and antivirals, how would we get them to people? Hospital emergency rooms and clinics, already stretched beyond capacity in some cases, would be overwhelmed.
Can anything be done in the short term?
Unfortunately, there hasn’t been a lot of planning on this, nationally, in a country where the public health leadership is obsessed with bioterrorism. But a growing number of public health people around the world have been sharing ideas online for months. Recently, a new, collaborative problem-solving Web technology to trade ideas and expertise on the subject was launched with fluwikie.com, in order to help communities plan on a local level. You can go to fluwikie.com and find out what’s happening state by state. An influenza pandemic is not going to be like a natural disaster, in which supplies can be rushed to a single affected area. It’s going to happen everywhere, almost simultaneously, over a two-month span. So what we need to do is consider how we would care for people locally, where we might set up beds for people, how we might reactivate retired nurses. You have to plan for that now, not when the pandemic hits.
For more information or to share your expertise, visit www.fluwikie.com. This article first appeared in the Fall, 2005 issue of health sphere, the magazine of BU’s School of Public Health. Image of avian flu virus courtesy of the Centers for Disease Control/C. Goldsmith, J. Katz, and S. Zaki.