Early Calculations Show Swine Flu Hard to Transmit

May 03, 2009  ·  Michael Fumento  ·  Weblog

It SEEMS like swine flu isn't particularly infectious by looking at case numbers and consulting news stories that continue to find a strong link to Mexico. But there's a scientific way of measuring using what's called a "basic reproductive number."

That essentially means the measure of how many secondary cases a typical patient will cause in a population with no immunity to the pathogen. Keep in mind that as an epidemic progresses, the number drops because the pathogen finds fewer and fewer susceptible victims. That's why all epidemics can be roughly plotted on the shape of a bell curve. (When I wrote that about U.S. AIDS epidemic, I was called a fruitcake. AIDS subsequently followed the shape of a bell curve.)

The director of Mexico's National Center for Epidemiology and Disease Control, [told](<a href=) the Washington Post "According to the preliminary models, the reproductive number that we have in the Mexico City metropolitan area is 1.5," noting, "It's a number fairly low, and that's good news."

Indeed for SARS, which caused only 8096 cases and 774 deaths over a period of about 170 days (115 cases and 4.5 deaths per day), the figure was 3.0.

For other contagious diseases, according to the CDC, it's vastly higher: 6-7 for diphtheria, 12-18 for measles, 4-7 for mumps, and 6-7 for Rubella.

Most importantly for our purposes the basic reproductive number for seasonal flu seems to range from 1.5 to 3.0. (Although you do see much higher numbers.)

That means no swine flu pandemic. The WHO can label it a pandemic; they can also label it a wombat. But because it won't begin to approach the severity of worldwide seasonal flu (700 - 1,400 deaths daily, it will not be a pandemic. Flu pandemics are supposed to be MORE severe than typical flu years, not far less.

And that's the end of it, right? Not necessarily. And here's where you see a difference between the know-it-all alarmists and a careful anti-alarmist.

Flu, like polar bears and penguins, loves cold weather. It's no more dangerous then, but spreads far more easily. If swine flu is still bouncing around in October, it will probably spread far more efficiently and quite possibly at the same rate as seasonal flu - though there's no reason to think it will be any higher.

That's why I called for making swine flu one of the strains in the annual seasonal flu vaccine. Unfortunately, that vaccine is already being grown in a laborious process using chicken eggs.

So the WHO and the CDC must decide whether swine flu merits the expensive creation of a whole separate vaccine, perhaps with a relatively new process using cell cultures instead of eggs. Considering how much money the U.S. threw away on pandemic avian flu ($5.6 billion; worldwide daily average of zero cases and zero deaths), it seems at this point they probably should.