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Friday, November 05, 2010

A Photon in the Darkness: Three Popular Anti-vaccine Myths Deconstructed

I love when people take to task the lies and distortions of the anti-vax pro-disease nutters.  While I don't think these are the most prevalent or the ones that cause parents to willingly subject their children to the dangers of infectious diseases that can kill them, they are the sort of things that anti-vax pro-disease nutters will go on about at length.  So, A Photon in the Darkness deconstructs them (pay attention to point 2, will be posting about that in a second):

Three Popular Anti-vaccine Myths Deconstructed

Anyone who spends any amount of time dealing with autism will eventually (usually within the first 24 hours) run into the mythical “vaccine-autism connection”. I say “mythical” because, much like its cousin the Loch Ness Monster, the “vaccine-autism connection” is much talked about and even widely believed without any solid data supporting its existence.

Since this is “Vaccine Awareness Week“, I thought I’d try an address at least a few of the other myths about vaccines (after several sharp jabs from readers prodding me in that direction).


[1] “You claim that vaccines are 100% safe and effective!”:
It seems that whenever I get into a discussion - face-to-face or virtual - about vaccines, someone will point out that vaccines have risks associated with them. This, strange as it may seem to some people, is not unknown, even among those who generally support the widespread use of vaccines.

Every real medical intervention has risks. I say “real” because there are a number of “non-real” medical interventions that are essentially risk-free (apart from the risk of using them instead of real medical treatment to treat a real illness) - homeopathy being the best example. Apart from the risk of choking, true homeopathic remedies (as opposed to “alternative” medicine remedies that are marketed as homeopathic but have measurable amounts of active ingredients) are about as risk-free an activity as you can engage in on this planet. They aren’t going to help you, but they are exceedingly unlikely to hurt you.

Back to the point, real medical treatments carry real (if usually very small) risks of death or injury. Vaccines are not an exception to this rule. What real medical practitioners look at is the risk-benefit ratio. The risk of death or injury from a vaccine is less - often millions of times less - than the risk from the disease it is produced to prevent. This is actually better than the risk-benefit ratios from most antibiotics, where the risk of serious allergic reaction is often cited as one in ten thousand or so [1].

So, what’s the myth?

The myth - as it is usually stated - is that people who support the widespread use of vaccines, including the use of vaccines in children, are claiming that vaccines are 100% safe. An variation on this them is that supporters claim vaccines are 100% effective.  Neither myth is true, either about the vaccines or the supporters of vaccines.

This myth is a straw man fallacy. The people using it are trying to find an easier position to argue against (one that their “opponent” doesn’t actually support) because trying to refute the actual argument - that vaccines are safer than going unvaccinated - would be hard. “Hard” as in impossible.

 No medical treatment is 100% safe or 100% effective - not one. Anyone who makes that claim is sadly misinformed (or is lying). And anyone who claims that someone else is making that claim had better be prepared to show proof.

[2] ”Vaccine-preventable diseases were in decline before the vaccines were introduced”:
Another popular vaccine myth is that vaccine-preventable diseases were disappearing even before the vaccines were introduced because of improvements in hygiene, nutrition or just about anything except vaccines. I’ve seen this ancient canard trotted out for both polio and measles in recent years. The usual “data” used to support this claim are the mortality figures for the disease in the years preceding introduction of the vaccine.

The key to this myth is the use of mortality data rather than incidence data. Although the myth is that the incidence of the disease was waning prior to the vaccine, the data show something very different: that the number of deaths attributed to the disease were declining.

So, how is this different, you might ask?

Let’s take a look at measles, as an illustration. When you look at a graph of reported measles cases (incidence), you will see a dramatic drop immediately after the vaccine was introduced [2]. Further, if you “scroll back” through the years preceding the vaccine, you’ll see that the number of cases was consistently high. This is only sensible, since measles is highly contagious and, prior to the vaccine, 95+% of the population had it by adulthood.

So, what about the graphs that show the measles mortality gradually drifting downward long before the measles vaccine? Well, most of them seem to be derived from the information presented in a 1975 paper by Engelhardt et al [3]. In this paper, the authors have a graph of measles mortality and measles incidence from 1912 to 1975. It’s figure 1, on page 1167. I’ll wait while you go look at it.

 Back already?

As you look at this graph, there are two things you should note: first, the vertical axis (the “Y” axis) is logarithmic. Second, you should note that while the incidence of measles (the number of cases per 100,000 population) didn’t show any overall decline until after 1963 (hint: the measles vaccine was introduced in 1963), the mortality rate (number of deaths per 100,000 population) was declining by the 1920’s (and possibly earlier).

So, does this mean that the claim that measles was already on the way out long before the vaccine was introduced is correct?

No.

The incidence of measles was unchanged until after the introduction of the vaccine, which shows that whatever advances there had been in hygiene, nutrition, etc. had no impact on the incidence of the disease. However, it does show that something - better hygiene, better nutrition (although that fails to explain the continued decline in mortality during the Great Depression), better medical care, better reporting of measles cases, etc. - gradually decreased the case-fatality rate (number of deaths per case of measles) from over 20 per 1,000 cases in 1912 to less than 1 per 1,000 cases in 1963 (from the graph in figure 1).

Anyone who wants a more in-depth discussion of the impact of the measles vaccine on measles incidence and mortality should check out two now-classic papers by RM Barkin [4][5].

As it turns out, the myth that “better hygiene (etc.) was eliminating measles (et al) before vaccines” is largely based on a classic “bait and switch” - they are claiming that there was a decline in disease incidence but only show data about disease mortality. In fact, while better hygiene, nutrition and whatever were clearly reducing the mortality rate of measles before the vaccine - at a rate of approximately one order of magnitude (factor of ten) in 20 years - the introduction of the measles vaccine reduced the mortality rate by another order of magnitude within five years after it was introduced.

No matter how you slice the numbers, introduction of the measles vaccine had a tremendous effect on measles, even if you only look at mortality. When you look at the actual incidence of measles, there is simply no room for doubt: the vaccine effectively ended measles outbreaks in the US (until a certain British doctor muddied the waters - but that’s a topic for another day).

[3] “The chickenpox vaccine causes shingles!”
[Note: the terminology of human herpes virus 3 infections is a bit confusing, primarily because the primary infection (varicella or "chickenpox") and the secondary infection or reactivation (herpes zoster or "shingles") were thought to be different diseases until 1964. The virus is alternately called varicellovirus, varicella virus, varicella-zoster virus, herpes zoster virus or human herpes virus 3 (HHV-3); I will call it human herpes virus 3 (HHV-3), in keeping with the current semi-standard in virology.]

I most recently saw this myth on Dr. Joseph Mercola’s medical parody website, where he wrote one of the most humourous statements about virology I have seen in a long time:
Chickenpox and shingles are related. They are caused by similar viruses, both in the herpesvirus family. After you recover from chickenpox, the virus can remain dormant (”asleep”) in your nerve roots for many years, unless it is awakened by some triggering factor such as physical or emotional stress. When awakened, it presents itself as shingles rather than chickenpox.[emphasis added]“
“Chickenpox” (varicella) and “shingles” (herpes zoster) are, in fact, caused by exactly the same virus (human herpes virus 3 or HHV-3). I suppose it could be argued that they would then be, of course, very similar - as similar as my right hand is to my right hand. Although Dr. Mercola is rather ambiguous in his wording, he is correct that after a primary HHV-3 infection (i.e. “chickenpox”), the virus does remain in the cell bodies of the dorsal root ganglia of your spinal cord. What “awakens” (reactivates) this dormant virus - according to available data - is a decline in immunity against the virus, which can be the result of a number of things:
[a] time - without recurrent stimulation, the immunity naturally declines over time.

[b] immune suppression - whether from infection (e.g. HIV, wild-type measles), disease (e.g. lymphoma, leukemia, etc.), medication (e.g. steroids, chemotherapy, etc.) and - yes - even that vague and ill-defined “stress”, immune suppression reduces immunity.

[c] age - the immune system ages along with the rest of the body, even if you are taking “supplements” and eating the right foods and getting proper exercise.

Let’s take a closer look at [a]: time. One of the features of the human immune system (when it is working properly) is that it doesn’t maintain an immune response indefinitely in the absence of continued challenge. This is part of the “check and balance” (or “yin and yang”) nature of the immune system, balancing stimulation and suppression to keep from under- or over-responding to foreign substances.

What we are finding with so-called “life-long immunity” to chickenpox (and measles, mumps etc.) is that at least part of the extended duration of this immunity is the result of periodic re-exposure to the virus. In pre-vaccine days, almost everyone got these diseases as children and those that survived were immune - for life, we originally thought. It turns out that this “life-long” immunity relies on periodic exposure to the virus - a “natural booster”, in effect.

In the days when 90+% of children had chickenpox at some point, there was no shortage of runny noses, uncovered sneezes and aerosolised crusts (from the lesions) to provide a timely inocculum for surrounding adults. However, even in those blissful days before the chickenpox vaccine, a certain percentage of otherwise healthy adults experienced a sufficient decline in their immunity to HHV-3 that they experienced a secondary (or reactivated) infection - known popularly as “shingles”.

The rash in shingles looks just like the chickenpox rash except that it is generally restricted to the distribution of one (sometimes more) sensory nerve root. Unlike the primary infection (”chickenpox”), however, the sensory nerve root is damaged - sometimes permanently. Patients experience this as the burning, stinging pain of shingles or - if they are unlucky - permanent post-herpetic neuralgia. If the nerve involved is the ophthamic branch of the trigeminal nerve, blindness is a very real possibility.

It is the prevention of shingles and post-herpetic neuralgia that make the chickenpox vaccine doubly important. While the mortality and diability rates from HHV-3 primary infection (”chickenpox”) are low (but not as low as the mortality and disability rates from the vaccine), the incidence of post-herpetic neuralgia from the secondary infection (”shingles”) is nearly 6 per 10,000 population per year [6].

Enter the chickenpox vaccine. One of the major differences between the HHV-3 vaccine strain and the wild-type is that the vaccine strain isn’t readily passed from person to person (the wild-type virus is highly contagious, as most parents of older children probably remember). Although some people may be inclined to doubt this, the fact that we are seeing an increase in adult shingles cases [7][8] - as Dr. Mercola correctly notes - is proof that the vaccine strain isn’t passed between people [see note below]. Let me explain why we can say that.

[Note: transmission of the chickenpox vaccine strain from recently vaccinated children to severely immunocompromised patients or from immunocompromised patients to healthy non-immune caregivers has been reported a number of times. However, transmission between immunocompetent people has been detected only rarely and usually in the presence of chronic illness [*] or between young siblings [**][***]. Thanks to Science Mom for pointing out this omission.]

We know that the HHV-3 vaccine strain, when given to older adults (the risk of shingles rises dramatically after age 50 as immunity declines - this was true even before the chickenpox vaccine) reduces the incidence of shingles [9]. We also know - as I mentioned above - that the incidence of shingles is increasing despite near-universal childhood vaccination with the chickenpox vaccine. If the vaccine strain was readily communicable, we wouldn’t see the rise in shingles because adults would be getting their “natural booster” from vaccinated children.

And before Dr. Mercola or some else claims that the rise in shingles cases are due to primary infections of adults with the vaccine strain, remember that the primary infection - with the wild-type HHV-3 or the vaccine strain - causes a generalised (over the whole body) rash, not the limited, dermatomal rash of shingles [Note: the rash is very mild to undetectable with the vaccine strain, although in immunosuppressed patients, the vaccine strain can cause an illness identical to wild-type HHV-3]. We also have evidence that the HHV-3 vaccine strain, when it is reactivated, will not cause the nerve damage that makes shingles (wild-type) so debilitating [10].

So, yes, the chickenpox vaccine is leading to a rise in shingles, but not in the way some people might want you to think. The good news is that the same vaccine that is “causing” the problem (by reducing exposure to wild-type virus - a good thing if you’re immune suppressed) can be used to “cure” it. In addition, if we are diligent about vaccination, it might be possible to eradicate HHV-3 (wild-type) and prevent future generations from having to suffer from shingles and post-herpetic neuralgia.

Summary:
This is just a taste of some of the many myths about vaccines that you can find on the Internet and in your community. If I had the time (and you had the patience), this could have easily been extended to the top three thousand anti-vaccine myths. As always, I encourage people to be skeptical of any sources of information that don’t “show their work”, especially if you agree with them. My references are below, if you want to check my work. I especially recommend [6] for those who are concerned about the chickenpox vaccine.

Prometheus

References:
[1] International Collaborative Study of Severe Anaphylaxis. Risk of anaphylaxis in a hospital population in relation to the use of various drugs: an international study. Pharmacoepidemiol Drug Saf. 2003 Apr-May;12(3):195-202.
[2] Meissner HC, Strebel PM, Orenstein WA. Measles Vaccines and the Potential for Worldwide Eradication of Measles. Pediatrics. 2004 Oct;114(4):1065-1069.
[3] Engelhardt J, et al. Measles Mortality in the United States 1971-1975. Am. J. Public Health. 1980;70(11):1166-1169.
[4] Barkin RM. Measles mortality. Analysis of the primary cause of death. Am. J. Dis. Child. 1975 Mar;129(3):307-9.
[5] Barkin RM. Measles mortality: a retrospective look at the vaccine era. Am. J. Epidemiol. 1975 Oct;102(4):341-9.
[6] Bennett GJ, Watson CP. Herpes zoster and postherpetic neuralgia: past, present and future. Pain Res. Manag. 2009 Jul-Aug;14(4):275-82.
[7] Jardine A, Conaty SJ, Vally H. Herpes zoster in Australia: evidence of increase in incidence in adults attributable to varicella immunization? Epidemiol. Infect. 2010 Aug 23:1-8.
[8] Patel MS, Gebremariam A, Davis MM. Herpes zoster-related hospitalizations and expenditures before and after introduction of the varicella vaccine in the United States. Infect. Control Hosp. Epidemiol. 2008 Dec;29(12):1157-63.
[9] Schmader KE, et al. Effect of a zoster vaccine on herpes zoster-related interference with functional status and health-related quality-of-life measures in older adults. J. Am. Geriatr. Soc. 2010 Sep;58(9):1634-41.
[10] Gutzeit C, et al. Identification of an important immunological difference between virulent varicella-zoster virus and its avirulent vaccine: viral disruption of dendritic cell instruction. J. Immunol. 2010 Jul 1;185(1):488-97.
[*] Grossberg R, et al.  Secondary transmission of varicella vaccine virus in a chronic care facility for children. J. Pediatr. 2006 Jun;148(6):842-4.
[**] Brunell PA, Argaw T. Chickenpox attributable to a vaccine virus contracted from a vaccinee with zoster. Pediatr. 2000;106:e28.
 [***] Otsuka T, et al. Transmission of Varicella Vaccine Virus, Japan. Emerg. Infect. Dis. 2009 Oct;15(10):1702-3.

 

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