How Bad is the Threat of Avian Flu? That Depends on Where You Live!

The Avian Influenza pandemic is less of a threat to the United States than it is to the developing world.

Think about the threat in terms of the number of people to get the disease, the number of those people who get very ill, and the number of the very ill who die or are left with permanent disability.

Flu epidemics can infect one in six, or even one in five in the entire population. One factor in the number of people infected relates to the flu virus itself. The current avian flu viruses appear to be very effective in infecting birds, but do not seem to pass easily from person to person. It is feared that the virus will evolve into something that is much more infective.

The transmission probability from person to person depends not only on the virus, but on the contact rates between people. Good housing and good hygiene can cut the rates significantly. The United States has an educated population who are relatively easy to reach with hygiene messages, good housing, a relatively uncrowded population, universal access to soap and water, and sufficient affluence to allow the sick to limit their contacts with others. The poor majority of the world’s population have none of these advantages. Indeed, crowding affects a much greater fraction of the world’s population that it did at the time of the Spanish flu epidemic of 1917.

The bird flu has killed about half of the people diagnosed with the disease. It is expected that if the virus population evolves into something capable of causing a pandemic, it will become less lethal. Still, people fear that two to three percent of those who come down with the disease would die of it. These numbers are awesome! If 20 percent of the world’s population got sick in a year, and three percent of those died, the death toll would be 36 million. A pandemic could sweep the world in two or three successive years – say a death toll of 108 million! This is a worst case scenario, and I suppose the death toll would be much less. Still, even a 15 percent incidence with a one percent death toll in a single year would be 9 million, a fearsome number of deaths!

A respiratory disease that makes people very sick, very fast and kills half of its victims is not likely to spread as fast as one that allows its victims to continue their daily activities, and immobilizes or kills only the most susceptible. The worst case scenario is a virus population that spreads easily but also makes a significant portion of its victims very sick, and kills many of them. The annual flu epidemics are major public health events, but one can hope that an emergent strain of avian influenza that does not represent a worst case scenario.

Preexisting immunity can reduce the numbers of people who get the disease, and the seriousness of the disease for those who do get it. That is why we immunize vulnerable populations, such as the old or those with certain chronic conditions such as diabetes. Many if not most people have some antibodies to the currently circulating flu viruses, even if not vaccinated, because they have been infected at some time in the past. This would not be true for a new avian flu strain if one emerges in the human population.

Fortunately, the United States appears well on the way to developing a vaccine for use in humans against the flu virus currently circulating in birds in Asia. President Bush has proposed stockpiling a large supply of this vaccine. In the case of the swine flu campaign undertaken in 1976, it turned out that the hoped for vaccine was not suitable for children; we may find that the current tests don’t justify the hope we have for the candidate vaccine. More than that, there is no way to estimate the efficacy and effectiveness of this vaccine against a strain of the virus that has not yet emerged as a threat to public health. Still we can hope! Even if a useful vaccine is developed in time, it must be widely used. This will be difficult to accomplish in rich countries. It will be more difficult still in poor countries with limited economic resources, and with limited health service capacities.

Tamiflu (oseltamivir) can be used with the currently circulating flu virus to reduce the severity of symptoms and the duration of the disease. Regular doses for well persons would seem to reduce the likelihood of getting flu. But the drug is in short supply, and much larger amounts are needed as a preventive treatment than as a drug for the treatment of the disease. The likelihood of poor people in developing nations getting much Tamiflu seems low to me! WHO seems to be suggesting that it be stockpiled, and rushed to sites where a local infection breaks out to create a circle of resistance, and thus prevent the triggering of an epidemic. I hope that this would work, but it seems to me to require more than the health systems of many poor countries could be expected to produce.

The threat of a flu pandemic is increased, as compared with the historical situation, by a number of “host factors”. There are more old people than there were in 1917, not only totally, but as a portion of the population, and the old are at greater risk. The HIV positive population, numbered in the tens of millions worldwide, are people with compromised immune systems who are at high risk. There remains a global hunger problem, and the malnourished are at high risk. Chronic diseases such as diabetes are epidemic, and their victims too are at increase risk. Clearly, many of the factors that increase people’s risk for the flu are more prevalent in poor than in rich countries.

Finally, medical services have come a long way in the United States and other developed nations since 1917. Even if we don’t have an effective flu nor enough of the drugs that reduce the virulence of a flu infection, we have antibiotics that can reduce the likelihood of bacterial complications of the flu, and supportive therapies that can help sustain life through a crisis of the disease. Currently, hundreds of thousands of people are hospitalized to receive such therapiesfor the flu each year in the United States. Indeed, one of the reasons for focusing preventive measures on front line health workers is so they will be available to help those who do get sick. And part of the economic fear relating to a pandemic is the cost of all the hospitalization that would be required if a large number of people get sick enough to require medical services (and of course the adequacy of existing medical systems to meet such a demand in addition to the demand for services for other diseases). Of course, poor people have less access to medical services than to the more affluent, and poor nations have already overstressed medical facilities.

We don’t know how likely it is that a virus will break out that is both able to infect large numbers of people and to make those infected very sick. In historical terms, such events have not happened more often than several times a century. The epidemic in birds has increased the likelihood that this will occur in the next few years. How high must such a probablity be to how much action? If we face one chance in 20 of a pandemic in the next three years? One chance in 10? One change in 100?

I hope that the world will mobilize to take preventive action, and that vaccines and anti-viral drugs will become available in time to fight against an epidemic of such a virus, if one does develop. I suggest, however, that in the worst case scenario, if a global pandemic does occur, its effects will be most severe in poor countries – those already most burdened by disease and poverty. I hope that the rich countries will not only strive to protect their own citizens, but will offer significant help to poor nations in Africa and Asia.