I’ve been writing about the H1N1 flu for the past few days, and have been asked repeatedly if the Centers for Disease Control (CDC) has reacted precipitously by ordering the production of millions of doses of vaccine and strongly recommending that individuals at highest risk get vaccinated as soon as possible.
To understand why the CDC has taken the aforementioned actions, you need a little background in history, epidemiology and virology. No one including the CDC knows what is going to happen, but they are using experience as a guide. Let me share (in a simplified form) what is known, then you can decide what you would do if you were the CDC.
History shows that the influenza virus, while typically mild, can mutate to forms that are deadly. The great influenza outbreak of 1918 (the Spanish flu) killed tens of millions of people. Curiously, the hardest hit were those who were young and healthy. They would come down with the flu, develop lung complications, and quickly drown in the fluid that filled their lungs. So although such outbreaks are uncommon, recent history shows that a flu outbreak can easily and quickly kill millions.
Epidemiology has shown us that two important factors are necessary for influenza to kill millions. The first factor is that the specific influenza virus must trigger severe disease. The second factor is that the specific influenza virus must be able to spread person to person.
Influenza also occurs in bird, and pigs, among other animals, and it probably jumped to humans thousands of years ago when they domesticated animals. Various influenza viruses can still jump easily from animals to people. However, when that happens, the disease, which may be quite severe, is self limited. In our increasingly urbanized world, very few people have direct contact with animals. Those who do may pick up dangerous strains of influenza and may die of them, but they won’t pass them on to other people, and no epidemic will develop.
Virology holds the third, and perhaps most important clue. When we think of genetics, we think of offspring inheriting genetic material from parents. Viruses (and bacteria) can exchange genetic material with each other. If both your parents have blue eyes, you might have blue eyes, too. Imagine, though, if you could acquire blue eyes simply by standing next to someone who has blue eyes. Viruses can acquire new traits that way.
The “perfect storm” in the world of influenza viruses is when a virus that is particularly deadly in animals comes in contact with a virus that can easily be transmitted from one human being to another. When that happens, the result can be a new virus that is particularly deadly and is now contagious.
Fortunately, that “perfect storm” does not occur very often, but the possibility always exists that it will happen. The CDC is greatly concerned that the new H1N1 variant of influenza is a “perfect storm” virus. It has the three deadly characteristics that we would expect in such a virus: it is new, so people are not immune to it; it can cause severe illness and death; and it is contagious from person to person.
Viruses can mutate very rapidly. For that reason they can become more dangerous, but they can also become less dangerous. No one knows what is going to happen with H1N1.
So we know the virus is here and the virus is lethal. What should we do about it?
We could do nothing and wait to see what happens. The virus could become less deadly and the danger will be over. Of course, the virus could remain lethal or even become more lethal as it is transmitted from person to person.
You can think about it as if it were a house fire. The fire could burn out of its own accord. It could burn down only the house involved. Or it could jump to neighboring houses and burn them down, too. In fact, fire, like viruses, tends to expand exponentially. It doesn’t jump from one house to the one next door. It jumps to all the houses nearby and then jumps to the all the houses near those. Pretty soon, the entire town is on fire. So waiting to see what happens makes as much sense as waiting to see if a house fire goes out on its own. It means taking a terrible risk.
In the case of viruses, as in the case of fire, prevention is the best strategy. Obviously it’s better if the fire never gets started in the first place. Similarly it is better if no one else gets the H1N1 strain of influenza. Vaccination is the only way to protect people from getting the disease. So vaccination is the first and best line of prevention.
In large fires, firefighters don’t simply attempt to save the houses already on fire. They try to set up firebreaks to prevent the spread of fire before it happens. Vaccination, in addition to preventing individuals from getting sick, also acts like a firebreak. If everyone around an infected person is has been vaccinated, no one can catch the virus. The spread of the virus is stopped cold. Vaccination protects not only those who are vaccinated, but everyone else in the population.
So imagine you are the head of the CDC. You know that H1N1 is here, and it is a particularly deadly form of influenza. You know that it can be passed person to person. And you know from history that similar viruses have killed 10 of millions of people in one epidemic. What would you do? Would you wait to see what happened? Or would you vaccinate against the disease and hope to save lives and halt the spread of the virus?
