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Home » Whooping cough outbreak – science and simple math

Whooping cough outbreak – science and simple math

I have written extensively about several whooping cough (Bordetella pertussis) outbreaks which had reached epidemic levels in areas like the Washington state, which had been considered one of the worst outbreaks in the USA during the past several decades. This whooping cough outbreak has lead to several deaths here in the USA and in other countries such as the UK.

Of course, these outbreaks and epidemics have lead to the “blame game” from the antivaccination cult, because they have claimed 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.

There have been numerous reports about a whooping cough outbreak in the Reno County, KS area, with about 70 cases of the disease being reported. The report indicates that most of the kids who have the disease were vaccinated. It is unclear who said this, and what are the actual statistics. But for now, we’ll take this at face value.

Since this outbreak will undoubtedly lead to the typical antivaccine rhetoric about the whooping cough vaccines, DTaP or Tdap (which also protect against tetanus and diphtheria), I decided to search the internet to find the most popular vaccine denialist arguments regarding pertussis vaccinations–then debunk them. Hopefully, this will be useful for those who are observing what’s going on in Reno.

Dr. Joe Mercola

Probably the most vociferous arguments made against the whooping cough vaccines come from Joe Mercola, one of the leading propagandists of the antivaccination movement, who decided to misinterpret data, probably intentionally, to condemn the use of the of the vaccine. He based his opinion on a 2010 whooping cough outbreak in California. Here’s what Mercola, the amateur and ignorant 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. With the Reno outbreak showing a similar number (that most of those who contracted whooping cough are vaccinated), Mercola’s comments might ring true with some.

Mercola is referencing this 2012 study published in Clinical Infectious Diseases. Or should I say “misreferencing.” Because, as Orac said in Joe Mercola attacks vaccinations again. Film at 11.:

[infobox icon=”quote-left”]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.[/infobox]

What published clinical studies say

In fact, the authors of the Clinical Infectious Diseases study concluded 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 make this clear as possible–this study is completely and intentionally misinterpreted by Mercola. In fact, 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 authors of the study recommend that 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, then come to a new and improved scientific consensus.

Just in case you think I’m inventing this stuff, another study in the Journal of Pediatrics, published in May 2012, came to  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 among the vaccine denier crowd–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.

Simple math about vaccination

Now back to Mercola’s comment about “only eight percent of those stricken were unvaccinated.” I had written 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 raw numbers of those whom were infected would be larger in a vaccinated group, since the vast majority of individuals are vaccinated, though it would be fallacious that being vaccinated was the underlying cause of becoming infected.

As I’ve written previously, looking at the raw numbers is an improper way to analyze these outbreaks. It’s the rate of incidence that matters. So let’s look at the simple math for this Reno whooping cough outbreak in some detail:

  •  There are about 16,000 children in Reno County under the age of 18 who might be at risk for whooping cough.
  • According to the CDC, the DTaP uptake is around 79% (that only includes those receiving the full 4 doses of the vaccine) in Kansas, so we’ll assume that it’s the same in Reno County. So that means 12,640 kids are fully vaccinated, and 3,360 are not.
  • Thought I don’t have any information about the vaccination status of the 70 presumed whooping cough patients, the news article seems to imply most were vaccinated. So, to make this as fair as possible, I’ll assume that 50 were vaccinated, 20 were not.
  • Based on my assumptions, the risk for contracting whooping cough for the vaccinated children is about 3.9 in 1000.
  • The risk for contracting whooping cough in unvaccinated children is about 5.9 out of 1000.

Thus, there’s about a 50% higher risk of contracting whooping cough if one is NOT vaccinated. Yes, if you’re just going to jump on the raw numbers, then it appears that the vaccinated are at higher risk. But they’re not.

One more point. These numbers are so small that it’s difficult to find anything meaningful in them.

So let’s examine a more detailed analysis of the recent Washington state whooping cough outbreak which 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. I’m almost ready to categorize antivaccination gangsters as math deniers.

Thanks to the Facebook group, Refutations to Anti Vaccination Memes.
Thanks to the Facebook group, Refutations to Anti Vaccination Memes.

More simple math

In a recent article by Barlow et al. (and an accompanying editorial by Mertsola) in the journal Clinical Infectious Diseases, data from the Oregon outbreak of pertussis during 2010-2012 showed that children immunized with acellular pertussis vaccine had less severe illness and significantly reduced whooping cough illness duration. So even though the vaccine is not perfectly effective, the vaccine makes an actual infection less problematic.

The researchers, led by Amy D. Sullivan, PhD, MPH, of the communicable disease services at Multnomah County Health Department in Portland, OR, thoroughly examined 753 case reports of pertussis from 1 August 2010, to 31 July 2012, to ascertain the effectiveness of acellular pertussis vaccines. Of the 753 patients, 633 were aged 6 weeks to 18 years. Moreover, 98.7% had vaccination history and illness data.

Below is the vaccination status of the group who caught pertussis :

  • 27% of the patients were not up-to-date with their vaccines
  • 46% were completely up-to-date.
  • 93% of the who had received at least one pertussis vaccination had received only the acellular version of the vaccine (as opposed to the discontinued whole cell vaccine).

The authors found that the odds of hospitalization and frequency of pneumonia were statistically decreased among all vaccinated patients, even those not up-to-date, compared to those who were never vaccinated. Furthermore, and most importantly, vaccinated (even those behind schedule) individuals were five times less likely to require hospitalization than unvaccinated individuals. Finally, vaccinated patients were 2.5 times less likely to develop a severe form of whooping cough compared to those who were unvaccinated.

This study confirms what many of us had suspected, that even if the pertussis vaccine isn’t 100% effective, it lessens the seriousness of whooping cough. So, let’s be clear, the vaccine generally does prevent most children from catching the disease. And, if they do catch it, it’s less severe. Sounds like a win/win.

And in case people forget, this disease isn’t some minor cough that can be ignored. Whooping cough can be a deadly disease that has significant complications for children:

  • 1 in 4 (23%) get pneumonia (lung infection)
  • 1 or 2 in 100 (1.6%) will have convulsions (violent, uncontrolled shaking)
  • Two thirds (67%) will have apnea (slowed or stopped breathing)
  • 1 in 300 (0.4%) will have encephalopathy (disease of the brain)
  • 1 or 2 in 100 (1.6%) will die

So anything we can do to protect our children makes sense. Because the pertussis vaccine saves lives.

Pertussis mutations–that old story

One of the consequences of the numerous whooping cough outbreaks over the past few years is that some people make unfounded claims that whooping cough has somehow mutated to avoid the immune response induced by vaccines. The irascible Orac attacks this one more point in a 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.

In a recent article in the New England Journal of Medicine, author James Cherry dismissed the pertussis 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.

The TL;DR version

So, let’s review the real scientific evidence:

  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-based medicine is almost always nuanced and honest–there are no absolutes.
  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.
Chart of whooping cough morbidity from 1922-2010.

There’s one more thing that the vaccine deniers fail to mention–vaccines work.

This graph illustrates 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.

Editor’s note – this article was original published in July 2015. It has been updated to fix broken links, improve formatting, and upgrading style.

Key citations:


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