05/29/2009 05:12 am ET Updated Nov 17, 2011

Understanding the Threat of a Flu Pandemic

Many headlines this week have covered the Swine Flu, a bug that has killed 80 people in Mexico alone. With little respect for borders, the flu has quickly spread to the United States, Canada, Europe and New Zealand.

What should you make of this alarming news?

Health officials are concerned by the appearance of this new swine flu because the jump from pigs to humans recently occurred, meaning people have no immunity to the bug, and the flu now appears capable of effective person to person transmission. That combination means the virus has pandemic potential. The last global epidemic occurred in 1918 during which 50 million people died. The actual number is a little hard to pin down, but experts give the range from 30 to 100 million as the final casualty figure; 50 million is the most often quoted. In any case, that flu killed more people than all previous outbreaks of the Plague, and more than the number of people who died in WWII. The potential for millions of deaths is what gives urgency to our response to the latest viral assault.

We could easily dismiss the warnings as a bit hysterical if we remember the 1976 outbreak of another swine flu. In that outbreak the first know victim, a healthy and robust soldier at Fort Dix, New Jersey, died within 24 hours of contracting the disease. Soon 500 of his compatriots fell ill. Given the aggressive nature of the infection, the federal government created an emergency inoculation program under which about 40 million Americans were given vaccines. Of those millions several hundred developed Guillain-Barré syndrome, a nasty induced-autoimmune disease in which the body attacks is own nervous system. The inoculation program was discontinued. An epidemic never developed.

More recently we had, and still have, the scare of H5N1, a bird flu originating in parts of Asia where people and poultry live in close quarters. This deadly virus appears to kill more effectively than any flu that has come before. Once the virus jumped from birds to people, little time passed before it could be transmitted from person to person, although the virus seems to pass between people inefficiently. That is, until a mutation removes that last barrier to a global outbreak. H5N1 cases have been confirmed in the United States, Asia, Africa, the Pacific, Europe and the Near East, Indonesia and Vietnam, but that global reach is not what is really eye-catching about this virus. Overall mortality in reported H5N1 cases is approximately 60%. To put that in perspective, the analogous number for the 1918 flu was 2.5% to 5%. Pause a moment to think about that. This virus is potentially 10 to 30 times more deadly than the virus that killed 50 million people. The incredible lethality of H5N1 led to a massive and concerted global effort to wipe out the reservoir for the virus by killing tens of millions of infected birds. The rapid and massive global response seems to have kept the virus at bay for now.

So given the seemingly false alarms with the 1979 swine flu and the recent arrival of H5N1, why should we believe health officials that this latest swine flu will cause us harm? Primarily because those outbreaks were not false alarms. Inoculating 40 million Americans was likely enough to prevent epidemic spread of the disease even after the program was discontinued. Without the vaccine program, the flu may well have infected a wide swath of the populace. Equally true, the massive globally-coordinated response to H5N1 with the destruction of millions of birds almost certainly prevented a pandemic, along with the fortuitous characteristic that the virus transmits poorly between people. The absence of pandemics in both of these cases does not mean that officials overreacted; instead it means that the actions they took likely prevented a much bigger outbreak. While proving a negative is difficult, prudence would dictate that we do not dismiss these examples simply because the actions taken effectively prevented a pandemic.

So, if we must take the new swine flu seriously, how much of a threat is it to us? To understand that we have to take a quick dip into the world of epidemiology. Scientists describe a disease using two primary characteristics: pathogenicity and virulence. Even the experts don't agree on exactly how these terms should be defined, but really they are easy enough to understand.


How easily a germ causes disease, and how readily it spreads, describes pathogenicity. If just one exposure to a few germs makes someone ill, that bug would be considered highly pathogenic. In popular use we often describe a pathogenic bug as being contagious -- that is, the virus or bacteria readily causes disease and easily spreads.


How severe the symptoms are once somebody gets sick describes a bug's virulence. In the most extreme examples of virulence, infection often leads to death. In that case we also discuss a bug's lethality -- which describes how many people who contract the disease die from it.

As an aside, not everybody would agree with my definitions. Some use virulence like I'm using pathogenic, or use the two terms synonymously.

With those two primary characteristics of pathogenicity and virulence we have four significant possibilities when we encounter a new bug: highly pathogenic and highly virulent; highly pathogenic and mildly virulent; mildly pathogenic and highly virulent; and mildly pathogenic and mildly virulent.

It could be, for example, that millions of people fall ill from a highly pathogenic virus that spreads rapidly through the population, but the symptoms of the disease are mild, say a runny nose and sore throat. That would be caused by a bug that is highly pathogenic but mildly virulent.

Or we could repeat what happened in 1918, where millions get sick, but instead of runny noses as the symptom, 60% of those infected die from hemorrhaging, dehydration, fever or massive organ failure. That outcome would be caused by a highly pathogenic, highly virulent virus.

With that knowledge in hand, we can now evaluate better for ourselves the threat of new viruses as they appear. You can now see the global concern for H5N1, one of the more virulent viruses described by scientists. Fortunately, because it passes poorly from person to person, for the moment at least, the virus is only mildly pathogenic -- it does not easily cause disease when one person exposes another to the virus. Yet. The real concern is that just one minor mutation could easily remove that barrier to transmission. In fact scientists believe that is exactly what happened in 1918. If that happens now with H5N1, we could see a pandemic that rivals 1918 in numbers of dead.

And you also can now understand the concern about the new swine flu, dubbed H1N1, an entirely new virus that is a mixture of bird, pig and human viruses. Unlike its cousin H5N1, the new virus indeed passes quickly and efficiently between people, even those never exposed to pigs or birds. So we know the bug is highly pathogenic. Unfortunately, H1N1 is also proving to be highly virulent, killing healthy young victims at alarming rates. We now face a virus, therefore, that is in the most lethal category, similar to what the world saw in 1918: highly pathogenic and highly virulent.

So do not dismiss health warnings. Do not pretend that officials can be ignored because they earlier issued "false alarms" that in fact were not. This is serious business. There is certainly no need to panic, but the potential threat is real. Therefore, the appropriate response is to be vigilant, to take prudent precautions, and to heed warnings issued by health experts.

You might, however, wish to dismiss those who claim that flu warning is a liberal conspiracy to push Kathleen Sebelius through the senate as Health and Human Services Secretary. Her nomination is being filibustered in the Senate by those who claim she is a "radical abortionist." If that conspiracy seems a bit over the top, Tony Perkins, President of the Family Research Council, has explicitly claimed that liberals are "scheming" to use the health "scare" to win confirmation. I suspect that Mr. Perkins would feel differently when infected H1N1. The bottom line is that Republicans are preventing the government from installing a leader at our national health agency in the midst of a potential crisis, all for short-term political gain. That parliamentary maneuver is the worst kind of cynicism one can imagine. Senate Republicans are using our health as a political football, ignoring the real threat from H1N1.