In another forum, I shared some very basic information on whooping cough. Recently, I was asked to post it in a place where it can be widely shared. So here it is!
Weekly Topic 02: Pertussis (Whooping Cough)
Thanks to the recent viral video of a baby with whooping cough, we’re doing pertussis this week.
In the United States, pertussis is currently the least well-controlled vaccine-preventable disease despite excellent vaccination coverage and 6 vaccine doses recommended between 2 months of age and adolescence. [E2]
What is whooping cough?
Whooping cough or “pertussis” is a coughing illness that usually lasts many weeks (“the 100-day cough”); when the child has the typical whooping cough symptoms, it’s called “classic pertussis.” Many pertussis infections are asymptomatic or present as the flu. For example, this study  found that among unvaccinated 10 year olds who had not had classic whooping cough, 64% had antibodies against pertussis toxin and 100% had antibodies against other pertussis antigens, indicating that 100% of unvaccinated children without history of whooping cough nevertheless had an infection but fought it off without symptoms. In this same study, they found that 61% of unvaccinated 10 year olds had had whooping cough, indicating that in a given population, about 60% will have classic pertussis and 40% will develop immunity by an asymptomatic or mild flu-like infection. Natural infection confers about 30 years of immunity , whereas the vaccine lasts at least one year for only 73% of recipients, and at least 2-4 years for only 34% . When symptoms do appear (i.e., when the child actually gets classic pertussis), it is most severe in newborns.
Whooping cough or pertussis is caused by one of several bacteria:
- Bordetella pertussis
- Bordetella parapertussis
- Bordetella holmesii
What is B. pertussis?
B. pertussis is the first bacteria we discovered that causes whooping cough. It was discovered in 1900 and is the only bacteria used for the whooping cough vaccine. Thanks to the vaccine, the bacteria has evolved and there are now two important strains to know about:
- Pertactin-deficient or “Non-PRN” B. pertussis is a new strain that makes up 85% of B. pertussis in the U.S. today . (EDIT: A later American study found 91.7% of tested B. pertussis isolates to be Non-PRN [E1]. However, this apparently varies by country and even by region within a country.) According to the CDC, those who are vaccinated are at higher risk of contracting this strain and the risk increases with more vaccine doses given . EDIT: This was later confirmed by other research in humans [E2] and experiments in mice [E3].
- PtxP3 B. pertussis is a new strain that produces more pertussis toxin and is therefore believed to be more dangerous. It was responsible for recent Australian outbreaks . It is believed that the vaccinated are at higher risk of contracting this strain . EDIT: This is supported by other recent research [E4]. Like Non-PRN B. pertussis, PtxP3 B. pertussis evolved in response to the vaccine. Since this strain first appeared right when whooping cough rates began increasing, it is thought to be the primary reason for the increased incidence of whooping cough [E5].
- EDIT: The prevailing theory seems to be that the increase in pertussis rates in spite of higher-than-ever pertussis vaccination rates is due to a combination of the vaccine wearing off and vaccine resistance due to Non-PRN and PtxP3 strains [E5].
What is B. parapertussis?
B. parapertussis is another species that causes whooping cough. It was discovered in the 1930s. The vaccine may increase the risk of infection with this species 40-fold .
What is B. holmesii?
B. holmesii is a new species that causes whooping cough. It was discovered in 1985. The pertussis vaccine may increase the risk of B. holmesii (DTP) or have no effect on the risk of B. holmesii (DTaP) .
What is the popularity of these species and strains?
Knowing how common the different species and strains are can help us predict vaccine-induced risk. A study in Ohio in 2010  found the proportions to be:
- 42.3% B. pertussis (or mix)
- estimated 36.0% Non-PRN
- estimated 6.3% PRN+
- 42.5% B. parapertussis
- 15.3% B. holmesii
The only species and strain against which the vaccine protects is PRN+ B. pertussis, which makes up approximately 6.3% of all whooping cough bacteria in circulation (if we take the CDC’s report that 15% of B. pertussis is PRN+). However, the vaccine has no effect on 15.3% of all whooping cough bacteria (B. holmesii) and increases your risk of 78.5% of all whooping cough bacteria (non-PRN B. pertussis and B. parapertussis).
Look up any recent news articles about whooping cough outbreaks. Although they frequently blame the unvaccinated, if they admit how many were vaccinated, it usually disproportionately affects the vaccinated.
EDIT: In fact, the CDC itself says that the unvaccinated are not responsible for the increase in whooping cough cases over the past few decades [E9].
What about herd immunity?
Because the vaccine is so ridiculously ineffective at preventing whooping cough—in fact, it increases your risk of whooping cough, as described above—there’s no such thing as herd immunity for whooping cough. However, even if the vaccine actually prevented whooping cough, it would not contribute to herd immunity because it does not prevent a person from becoming contagious.
A 2013 FDA study  found that after being exposed to an animal with classic whooping cough, vaccinated baboons got infected but did not have symptoms and were contagious. In other words, vaccinated people may be protected from developing classic whooping cough caused by PRN+ B. pertussis (which was the strain used in the study and the only strain against which the vaccine protects), but they are not protected against becoming infected and contagious. In this respect, the vaccinated may pose a greater risk to vulnerable people like infants and immunocompromised individuals because they are more likely to get whooping cough caused by newer species/strains and more likely to develop a contagious asymptomatic infection caused by the vaccine-targeted strain. If they have no symptoms, they do not know they are contagious.
ETA: The lead author of the FDA baboon study also gave the New York Times an interview in which he explained that the vaccinated still develop infection when they are exposed and grow the bacteria in the backs of their throats, and thereby are contagious. He described this as “good for you, but not for the population” [E8].
What about getting the vaccine during pregnancy?
Women who get the vaccine during pregnancy develop some antibodies and pass them on to their babies–about 68.8 U/mL [E6]. However, the level of antibodies required to prevent pertussis is 246 U/mL [E7]. Not surprisingly, it has not yet been demonstrated that infants who received the Tdap vaccine during pregnancy have reduced risk of pertussis.
What’s the bottom line?
Many pertussis infections are so mild that they are not recognized as pertussis. Furthermore, the pertussis vaccine offers no real protection. It increases your risk of almost 80% of whooping cough bacteria and protects against only 6%. It also makes you susceptible to becoming a contagious asymptomatic carrier. There is no evidence that getting it during pregnancy protects your baby.
UPDATE 9/16/16: Looks like the above link no longer works. Here’s an archived version of the link:
Please note that the exact proportions of species and strains differs from country to country, so the vaccine-targeted strain may make up less or more of the total in your region. The U.S. studies mentioned above should be used only as a rough estimate.