Skeptical Raptor's Blog hunting pseudoscience in the internet jungle

Effectiveness of pertussis vaccines–myth vs. reality

Note: an updated version of this article can be found here.

Over the past few months I have written extensively about the the current whooping cough (Bordetella pertussis) outbreak which has reached epidemic levels in areas like the Washington state, and has been considered one of the worst outbreaks in the USA during the past several decades. The outbreak has lead to several deaths here in the USA and in other countries such as the UK. Of course, this outbreak has lead to the blame game from the antivaccination crowd, because they claim that since A) most kids are vaccinated, and B) we’re having this outbreak then C) either the vaccines are useless or are actually the cause of the outbreak. Seriously. They blame the vaccines.

So I decided to search the internet (or just read the comments section of my blog) to find the most popular vaccine denialist arguments regarding pertussis vaccinations, and deconstruct and debunk them. Hopefully, it will be a useful tool for you when you’re engaging a ridiculous argument with one of those antivaccinationists. Of course, I could use the information too.

First, let’s start with Joe Mercola, Ground Zero of the antivaccination movement, decided to misinterpret data, probably intentionally, to condemn the use of the pertussis vaccine (DTaP or Tdap) because of 2010 whooping cough outbreak in California. Here’s what Mercola, the genius immunologist had to say about that:

In fact, the study showed that 81 percent of 2010 California whooping cough cases in people under the age of 18 occurred in those who were fully up to date on the whooping cough vaccine. Eleven percent had received at least one shot, but not the entire recommended series, and only eight percent of those stricken were unvaccinated.

That “only 8% of those stricken were unvaccinated” has been repeated over and over again by the vaccine denialists as proof that being vaccinated is more dangerous than not being vaccinated. Now Mercola is referencing this study published in Clinical Infectious Diseases published in March, 2012. Or should I say “misreferencing.” Because, as Orac said in Joe Mercola attacks vaccinations again. Film at 11., “Needless to say (but I’m going to say it anyway), Mercola is being disingenuous here. For one thing, the authors stated quite clearly: ‘In reviewing cases confirmed at our medical center during this outbreak, we noted effective protection of younger children.'” Once again, I guess if the vaccine denialists lack evidence, then invent it if necessary.

In fact the authors of the study conclude that:

In the case of the recent California epidemic, it appears that the effectiveness of the current vaccine schedule, when paired with the imperfect vaccination rate, may be insufficient to prevent an epidemic. Earlier vaccine booster doses may be required to provide adequate herd immunity, absent an increase in vaccination rate, efficacy, or durability. Earlier booster doses could prevent immunity from waning, and address disease in the 8-12 age group.

Let’s translate into clear English. This study doesn’t say anything like what Mercola said. The vaccine still works, but the immunity from it wanes sooner than expected, and that this area of California doesn’t have a high enough rate of vaccination to prevent epidemics. Moreover, the CDC and FDA should change the vaccination schedule to provide earlier boosters to protect older children and teenagers (and I would contend adults).  This is how science works, get the evidence, revise the hypothesis, and retest the hypothesis.

Just in case you think I’m inventing this stuff, another study in the Journal of Pediatrics, published in May 2012, makes essentially the same conclusion: it found an increase in pertussis among children aged 7-10 years who had completed the DTaP immunization but who had not yet received the Tdap booster recommended at age 11-12 years, along with a concomitant decrease in cases among adolescents from ages 11 to 14. The study concluded that preadolescents are subject to waning immunity with the current schedule but that the adolescent Tdap dose is effective in protecting younger adolescents.

But these two studies lead to the Nirvana Fallacy amongst the antivaccinationists–if the pertussis vaccine isn’t perfect, then it’s useless. We’ve already shown that the two studies have provided evidence that we need to adjust the vaccination schedule protect one group of later adolescents but is still effective in other groups of children. And even those with waning effectives were still protected.

Now back to Mercola’s comment about “only eight percent of those stricken were unvaccinated.” I wrote recently that the CDC has determined that around 95% kindergartners are up-to-date with their DTaP vaccine, so the population of those vaccinated against pertussis is obviously larger, and you can expect that given what was discussed above, the numbers who were infected would be larger in a vaccinated group, though it would be fallacious that being vaccinated was the underlying cause of becoming infected. However, a more detailed analysis of the Washington state epidemic shows exactly how the infection rate breaks out between vaccinated and unvaccinated groups by age group:

  • Ages 5-9 unvaccinated or under vaccinated children are 6 times more likely to become infected with pertussis than fully vaccinated. 
  • Ages 10-13 unvaccinated or under vaccinated are 25 times more likely to become infected with pertussis than fully vaccinated. 
  • Ages 14-18 unvaccinated or under vaccinated  are 6 times more likely to become infected with pertussis than fully vaccinated.

In other words, when you directly compare the likelihood of catching pertussis, it’s still much safer to be fully vaccinated than not. By the way, this is how science works again. Make valid statistical comparisons, not ones that are fallacious.

Orac makes one more point in a recent blog post:

…Mercola (claims) that vaccines are “causing dangerous mutations.” While it is possible that the B. pertussis bacteria is developing “resistance” to the vaccine through natural selection, the evidence that it is doing so strikes me as rather weak and preliminary. Even if it were, the answer would be to change the vaccine in order to include the altered antigens. After all, do we decide that antibiotics don’t work when bacteria evolve resistance or that chemotherapy doesn’t work when tumors manage to do the same? That’s a rhetorical question, of course. Some segments of the alt-med world do, but reasonable scientists do not. They work to overcome that resistance.

A recent article in the New England Journal of Medicine by James Cherry, Epidemic Pertussis in 2012 — The Resurgence of a Vaccine-Preventable Disease, more or less dismisses the mutation “hypothesis”:

Finally, we should consider the potential contribution of genetic changes in circulating strains of B. pertussis. It is clear that genetic changes have occurred over time in three B. pertussis antigens — pertussis toxin, pertactin, and fimbriae. In fact, changes in fimbrial agglutinogens related to vaccine use were noted about 50 years ago. Studies in the Netherlands and Australia have suggested that genetic changes have led to vaccine failures, but many people question these findings. If genetic changes had increased the rates of vaccine failure, one would expect to see those effects first in Denmark, which has for the past 15 years used a vaccine with a single pertussis antigen (pertussis toxin toxoid). To date, however, there is no evidence of increased vaccine failure in Denmark.

So, let’s review:

  1. The vaccine works, although the effectiveness may wane between boosters. There is no evidence that it has stopped working completely.
  2. The vaccine isn’t perfect. In medicine, perfection is a fallacy pushed by the alt med world. Real science is nuanced and honest. 
  3. Individuals who aren’t vaccinated are up to 25X more likely to contract whooping cough than those who are fully vaccinated.
  4. B. pertussis probably is not mutating to evolve resistance, but the evidence is a bit preliminary. Even if it is, we can develop new vaccines.

pertussis-chart-CDCThere’s one more thing that the vaccination denialists fail to mention. Vaccines work.

This graph represents the absolute number of pertussis cases in the USA, which shows a dramatic drop since the introduction of the pertussis vaccine in the mid-40’s. If this graph was converted into per capita, accounting for the nearly 2.5X increase of US population from the 1930’s, the drop would be even more dramatic. In other words, even with the what the antivaccinationists claim as a “bad vaccine”, pertussis is just about wiped out compared to what it was just 70 or 80 years ago. But, as you can see, the slight increase recently means that we have to vigilant, and we have to do some adjustments to the vaccine. Medicine does that all the time. I’m pretty certain that cancer therapies have evolved from 1930 to 2012. And that’s a good thing.

Vaccines save lives. That’s obvious.

Use the Science-based Vaccine Search Engine.

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