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h1n1: don’t make me go there… again
By | November 3, 2009
…oh, all right, i’ll go there one more time. i can’t even believe how many questions i get about the h1n1 flu shot. (and how few questions i get about the h1n1 flu disease – or the “regular” flu. i hate flu!)
last night one of those celebrity-worshipping tv shows delivered a halfhearted retraction about a video of theirs that had been recast on youtube*. the video showed a woman who developed neurological-motor problems after getting a flu shot (not h1n1, but “regular” flu). [the re-cast said 'you should worry' about getting shots, and the show said that what they meant was, 'you shouldn't worry'.] (beware of the remix!)
post hoc, ergo propter hoc: it happened after the thing; therefore, it happened because of the thing: a well-known logical fallacy. the classic example is, roosters crow before the sun comes up – therefore, roosters make the sun rise. but we know this is not true, however true it looks… correlation is not causation.
however, having something dreadful happen post hoc, can certainly give us the feeling that propter hoc! the real question is, how many so-called side effects can be expected to occur even in the absence of hoc? in other words, what are the odds of developing a neurological-motor problem (or a conversion disorder) even without getting a flu shot? this was the subject of an article reposted by kevinmd.com, concerning “background events” or illness/disability/disaster occurring at the usual “background” rates:
“Overall, 3.58 cases of Guillain-Barre syndrome would be expected as background events within seven days per 10 million individuals vaccinated and 21.50 per 10 million within six weeks.”
this means basically that there is a certain rate of people getting guillain-barre (“gee-yan bar-ray”) paralysis, even without getting a flu shot. it means that you can’t blame guillain-barre on the flu shot, in this certain number of people. see? even if you, or your auntie, or your neighbor’s teenage child, is one of them, and is real sick, and just got a flu shot the previous week. it’s almost certainly a coincidence.
“…Coincident sudden death [yikes!] would be expected to strike 0.98 people per 10 million vaccinated people within seven days of vaccination and 5.75 cases would be expected to occur within six weeks as background events.
“Among women, 14.40 cases of optic neuritis [sudden blindness!!] would be expected for every 10 million vaccinated within seven days and 86.30 could be expected for the same population within six weeks.
“For pregnant women, 397 spontaneous abortions [aaaa!] within one day of vaccination would occur as coincidental, background events for every 1 million vaccinated.”
it gets worse: the authors also discuss the problem of “temporal and geographical clustering” – the phenomenon that such illnesses/disabilities/disasters are not spread out evenly across time and space, but may clump up, so that a bunch of things appear to be happening in one specific place or time.
“For example, about 2% of [medical] practices will likely have a seemingly elevated rate – more than two standard deviations above average [that's high!] - of postvaccination spontaneous abortion, based on the normal distribution.” (“the normal distribution” is the “bell curve” of how events naturally spread out across large populations.)
what this means is that even a big cluster of illnesses/disabilities/disasters occurring in one place, after a vaccination campaign, may not have anything to do with the vaccinations themselves – any more than the sun can be raised by even by many, many, many roosters all crowing at once. it also means that you can’t take the figure “4 cases of guillain-barre per 10,000,000 shots” and turn it into “1 case per 2.5 million,” and then claim that 2 cases per 2.5 million is an elevated rate – except “on average.” if you see what i mean.
how much is 2.5 million? to get a sense of scale, note that the government/ taxpayers have purchased 100 times that many doses of h1n1 flu vaccine. or consider that 2 million is the number of folks, in oregon alone, who are considered high-risk first candidates to get the shot (though only a tenth of that many doses have been delivered so far, which is the real news story, if you ask me – the shortage.)
we realize, of course, that every medication (and supplement, and food, and activity) may have unintended risks. so how can we tell true side effects from post-hoc, apparent ones? due to tons and tons of public concern and the current ubiquity of high technology, the cdc is tracking “adverse event reporting” better than ever.
“…In the U.S., the voluntary Vaccine Adverse Event Reporting System has beefed up outreach efforts, and a new Web-based active surveillance system has been implemented along with population-based, computerized database monitoring… The CDC’s Frank DeStefano, MD, MPH, and Jerome Tokars, MD, MPH, wrote that other countries have mounted similarly intensive monitoring for the safety of the H1N1 vaccine, which should serve as a model for tracking safety of all vaccines in the future.”
so very shortly we will know more about the h1n1 shot, flu shots in general, and all shots in general.
but beware: from science-based medicine: “The Vaccine Adverse Event Reporting System is a voluntary reporting system that accepts all reports of symptoms or illnesses that occurred after vaccination. It even accepted a fraudulent report claiming that a man had been turned into The Hulk by his influenza vaccine.” (emphasis added)
dr leigh does not provide medical advice over the internets, unless you are her private patient communicating with her over secure channels. please do not ask her for diagnosis or treatment as a result of reading this article!
*for more, see here.
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