April 27, 2009
-- by Dave Johnson
The "swine flu" H1N1 virus is a potential pandemic flu that started in Mexico and is spreading. Pandemics, meaning influenza epidemics in multiple countries, happen every 20 years or so, and we are overdue. Flu pandemics are very serious. The Spanish Flu of 1918-19 had an estimated mortality rate of 2.5% and killed between 20 and 40 million people. The Hong Kong flu of 1968 had a lower death rate, killing 33,800 in the United States and 1 million worldwide.
The reason flu pandemics happen is that the influenza virus constantly mutates. Every year the new flu viruses are usually only a little bit different from the prior year, so even though we may get sick, some of us have some immunity and the existing antibodies (from earlier times we had flu or a flu vaccine) provide some protection. Public health organizations like the Centers for Disease Control and Prevention (the CDC) track the emergence of new viruses and usually have time to prepare the yearly vaccines. So usually the new flu strains don't hit as many people, and therefore fewer sick people are spreading it, and most people aren't getting sick to the point where death is a possibility.
But sometimes there is a major genetic shift, in which a flu virus appears that contains pieces from bird and/or swine influenza viruses as well a human virus. Humans have no immunity to this new virus. So the flu sweeps through the population, and those who get it get much sicker. The new Mexican swine flu virus contains a mixture of genetic material from swine, bird, and human influenza viruses.
These influenza epidemics can sometimes be very, very serious, like that 1918 Spanish flu. The recent "Bird Flu" human fatalities appeared to be over 60% , but it appears that the "bird flu" (avian influenza) was not easily transmitted from one human to another. However, if there is another small modification in the bird flu virus such that it acquired the ability to be easily spread between people, the result could be beyond catostrophic -- like the plague years. That is why bird flu was so much in the news. SARS (the Severe Acute Respiratory Syndrome), which was caused by a non-influenza type virus, killed 17% of humans it infected, but the epidemic was stopped before it spread widely. This new Mexican swine flu seems to be killing about 10% of the people it has sickened in Mexico, if the numbers are correct, but there is no way to know accurately yet.
Usually, influenza is more serious in the elderly and the very young, whose immune systems are weakers. However, pandemic flus, which are caused by novel new flu virus strains, are more deadly in stronger people (like young adults) than in the very old or very young, because it causes their stronger immune systems to overreact, called a "cytokine storm" -- a major release of infection-fighting substances in the body that can, in large quantities, cause serious damage. This extreme immune reaction is what makes pandemic flu so serious, and is the reason it strikes so much harder in healthy young people. It appears that this new Mexican flu is killing young adults--people of the right age--which is another sign it could be dangerous. On the other hand, there have been no fatalities yet in the United States, which is a promising sign. It may mean there is some factor involved in the cases in Mexico that aggravated the disease, that wasn't present in the US cases. Or it may mean that the flu spreading in the US is somehow different.
Note, when I search for "swine flu" on Google News I get lots of stories about how "the scare" is "affecting the markets." It's like how they cover movies, not according to whether they are any good, but how much money they make each weekend. So the major media mindset is still more concerned with money than people.
Posted by Dave Johnson at April 27, 2009 2:50 PM
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