DISCLAIMER: This blog post is not about pertussis vaccination overall. This blog post is about pertussis cocooning. Any rabbit trail I make is really meant to point back to the overall purpose of this blog post, which is pertussis cocooning. Did I mention this blog post is about pertussis cocooning? I now return you to your regularly scheduled program.
Jabs for Love
Some of my readers may be aware that I am pregnant and due to deliver in late May. I’ve recently been asked whether I want adults who plan to visit my newborn to get the whooping cough (pertussis) vaccine. This question probably arose from the CDC’s recent recommendation that adult contacts of a newborn get vaccinated so as to decrease the baby’s risk of contracting it from them , and from simple love—I love your unborn child and want to do everything in my power to protect him/her if I can—“jabs for love,” if you will. I generally answered privately because these days, if you express the slightest reservations over or even the strongest scientific evidence against any vaccine in any form for anybody or for any reason, you are labeled “anti-vaxx,” but I’ve been asked to share it more publicly.
Well, I would like to state that I’m not “anti-vaxx,” but I’m not sure what that label even means (nor “pro-vaxx” for that matter). And honestly, the medical profession (some of you may also be aware that I’m an ER nurse) has an equally vague term—“vaccine hesitant”—which is applied to anyone who hesitates over or questions the safety, efficacy, or necessity of any vaccine for all or for any unique individual. (For example, one of my coworkers in the ER was allergic to the flu vaccine. Because of her refusal to get one every year due to her allergy, she is technically “vaccine hesitant.”) In that case, I stand with the majority of nurses (Footnote 1) as “vaccine hesitant” due to my “hesitancy” over the influenza vaccine, which has basically been deemed worthless by a dozen Cochrane Reviews (Footnote 2). Over time, I’ve come to feel the same about the HPV vaccine, and I’ve rather recently discovered some things about the pertussis vaccine that makes me reconsider the wisdom of cocooning. And now, I’m going to put myself in mortal danger of being brutally murdered by “Big Pharma” or whoever it is “anti-vaxxers” are afraid of, by giving my answer to pertussis publicly rather than privately. Sharpen your pitchforks. 😉
Problems with Cocooning
I’ve seen some people suggest that the pertussis component of the adult TdaP (and pediatric DTaP) vaccine sheds, due to a misunderstanding of a certain FDA baboon study. This is not true. (The FDA news release  is vague and can easily be misunderstood to mean that, but if you read the study itself , it’s very clear, as I’ll discuss in my first point below.) If you stop to think about it, the TdaP (and DTaP) contains acellular pertussis (the aP portion), which includes only some of the components of the bacterium, not the entire bacterium. So how can you develop the growth of (be “colonized” or “infected” with) the bacteria when you’re only getting bits and pieces of it? (If someone gives you—but don’t ask me why they would—a cat’s tail and whiskers, can the cat come to life and claw you? Yes. …If you’re on LSD.) And if you can’t get an entire bacterium from the vaccine, how can you give an entire bacterium to someone else?
So I’m not afraid of the TdaP shedding and therefore won’t ask adult contacts of my newborn to avoid it for that reason. Because it just doesn’t make scientific sense.
However, although the TdaP doesn’t shed like live virus vaccines do, it:
1) Increases the risk that the recipient will become an asymptomatic carrier of B. pertussis following exposure and thereby infect others, as demonstrated in baboons in the aforementioned FDA study [2, 3] and in immunized children in an Israeli study reported by the CDC . The FDA study demonstrated that following exposure to an infected baboon, baboons who had been vaccinated with acellular pertussis (as in the TdaP and DTaP vaccines) became asymptomatic carriers for 6 weeks after colonization and baboons who had been vaccinated with whole cell pertussis (as in the DTP or DTwP vaccine) became asymptomatic carriers for 3 weeks after colonization. These asymptomatic carriers then infected other baboons, demonstrating that pertussis bacteria may leap from one asymptomatic carrier to someone who is susceptible to infection by the bacteria because they were low-responders to vaccination, non-responders to vaccination, no longer immune due to waning immunity from the vaccine, or unvaccinated (Footnote 3). It’s unknown whether the bacteria can leap from one asymptomatic carrier to another asymptomatic carrier until it infects a susceptible individual.
2) May make those who do get sick with B. pertussis have milder symptoms such as no “whoop” to their cough. According to the CDC, “Adolescents and adults and children partially protected by the vaccine may become infected with B. pertussis… Pertussis infection in these persons may be asymptomatic, or present as illness ranging from a mild cough illness to classic pertussis with persistent cough (i.e., lasting more than 7 days). Inspiratory whoop is not common.” [5, p. 216] Unfortunately, this makes it harder to diagnose and more likely they’ll infect others, as in a case affecting six infants in Texas [6, para. 1] and another case affecting four newborns in Australia , both of which involved immunized nurses who infected newborn babies with pertussis due to a failure of physicians to diagnose their atypical symptoms.
3) Increases the risk of pertussis infection (whooping cough) caused by non-PRN strains of pertussis (pertussis bacteria lacking pertactin, a key antigen in the vaccine), as reported by the CDC. Non-PRN strains now make up over 50% of all B. pertussis isolates and a study of 752 pertussis cases in 2012 found 85% were caused by non-PRN strains. Interestingly, the vaccinated who are up-to-date on their pertussis vaccinations are more likely to become infected by these strains than the unvaccinated, reflecting a tendency for these strains to selectively attack the vaccinated. [8, pg. 6]
4) And potentially increases the risk of contracting B. parapertussis, another cause of whooping cough, 40-fold [9, 10]. I say “potentially” because this study was done in mice.
Pertussis cases have increased in spite of increasing pertussis vaccination. The FDA states, “the rates of [pertussis] infection in the U.S. have been rising over the last 30 years, despite vaccination of over 95% of children nationwide. The U.S. is now experiencing levels of pertussis comparable to those seen in the 1950s, with 48,000 cases reported in 2012.” [11, para. 3] The above four points have all been suggested as reasons for this paradoxical increase.
The FDA also states that the effects of cocooning (vaccinating all of a newborn’s adult or other contacts, which is being implemented this year in the U.S.) are unclear . However, Australia, which had implemented cocooning efforts as early as 2009, abandoned it in 2012 because it was found to be ineffective at preventing pertussis infection in newborns .
So in summary, pertussis vaccination of adult contacts increases the risk of asymptomatic infection (increasing the risk of the infant contracting the disease); increases the risk of atypical symptomatic disease (again increasing the risk of the infant contracting the disease); increases the risk of infection and disease caused by the majority of pertussis strains (increasing the risk of the adult contact contracting the disease, therefore potentially increasing the risk of the infant contracting the disease); and potentially increases susceptibility to B. parapertussis (also increasing the risk of the adult contact contracting the disease, therefore potentially increasing the risk of the infant contracting the disease). Furthermore, cocooning has epidemiologically been found ineffective at preventing whooping cough in newborns.
So no, I won’t ask my family and friends to get vaccinated against pertussis. It just doesn’t make scientific sense.
I’m not going to tell you what to do for yourself. Getting any vaccine due to the perceived benefits to yourself, even very falsely perceived benefits as in the case of the influenza vaccine, is your choice.
However, if you want to get the vaccine solely in order to protect my child—don’t. According to the best scientific evidence from the FDA and CDC, and epidemiological evidence from Australia, you may actually be increasing my child’s risk of infection. Now, I’m not going to shriek, “Don’t visit my child if you have/haven’t gotten X vaccine, you horribleterribleawfulcrazyinsane person!!!” because I’m not ruled by fear, as are so many in these vaccine discussions. All I’m saying is that I will never ask you to protect my child by doing something that is more likely to harm him than to help him.
A Slight Rabbit Trail…
I think the pertussis vaccine is similar to the HiB vaccine. Once upon a time, B was the most common strain of Haemophilus influenzae (a bacterium, not a virus), accounting for over 80% of invasive H. influenzae disease in children, but now it’s significantly less common, having decreased by 99% in children (probably thanks to vaccination of children, which has also correlated to a decreased incidence of HiB in adults). Nowadays, the A and C-F strains are the most common, and the HiB vaccine offers no protection against those strains. Unfortunately, invasive H. influenzae disease, which carries a 22% fatality rate in adults, is increasing in overall incidence, probably as a result of the vaccine inadvertently shifting strain dominance from B, against which the vaccine offers protection, to strains A and C-F, against which it offers no protection . In other words, the overall effect of the vaccine has been to increase all-type H. influenzae infections in spite of a 99% decrease in type B infections, including a sharp increase in the incidence of dangerous invasive H. influenzae disease. So while HiB vaccination made sense when the vaccine was first introduced, and was associated with a sharp reduction in HiB infections (a good thing!), it now has the effect of increasing overall H. influenzae infection and invasive disease rates. It would make more sense today to vaccinate against HiF (the new most common typeable strain) or against all-type H. influenzae , if possible, than to continue use of a vaccine that increases the overall risk rather than decreasing it.
Similarly, the introduction of the pertussis vaccine in the U.S. in the 1930s correlated to a sharp reduction in whooping cough rates (Footnote 4). However, by a process of natural selection, the vaccine has resulted in different strains not included in the vaccine gaining dominance, and, for probably manifold and complex reasons we don’t yet fully comprehend, recently increasing the overall incidence of whooping cough infections.
Like the HiB vaccine, it may be time to either update or retire the pertussis vaccine. Should the pharmaceutical companies produce an HiF or all-type Hi vaccine and update the pertussis vaccine (and I had reason to believe in their safety and efficacy, unlike the HPV and influenza vaccines), I would be far more comfortable receiving for myself or my child or recommending to potential adult contacts of my newborn those vaccines than receiving the current HiB and pertussis vaccines, which seem to rather increase the risk and incidence of infection and disease than to decrease it.
I think I can already feel the pitchforks poking. 😉
Footnote 1: As recently as 2010, the influenza vaccination rate among healthcare providers was so low (30-50%) that the goal was only to get the rate as high as 60% by 2010 . In fact, “as a group, health workers are among the most poorly covered” as regards influenza vaccination  and the second most common reason given by healthcare providers for getting the flu shot is “My employer requires me to be vaccinated for flu” with less than half reporting that they think it will prevent them from getting influenza . Today, in an environment where influenza vaccination is often required as a condition of employment with few or no exceptions, the majority of nurses do receive the influenza vaccine at 90.5% in the 2013-2014 season , an increase from about 80% in the 2011-2012 season and from about 75% in the 2010-2011 season. This increase is largely attributed to employer mandates (in fact, a 2012 CDC report showed that mandatory vaccination in healthcare institutions raised compliance rates to almost 100%) rather than to a change in attitude regarding flu vaccination .
Footnote 2: For those who don’t know, the Cochrane Collaboration is a global, independent, nongovernmental organization that gathers, reviews, and summarizes the latest scientific knowledge from the highest quality research. Because they limit themselves to the highest quality research, and most published research today is very poor and/or biased , there are limits to the topics they can discuss. For example, the highest quality type of study is a double-blind, randomized, placebo-controlled trial (RCT), which means the participants are randomly assigned into one of two or more groups, at least one group gets a placebo (an ineffective treatment, such as a sugar pill or an injection of saline or water), and neither the participant nor the person administering the treatment knows whether they’re getting “the real thing” or the placebo. These randomization and double-blind placebo techniques eliminate as much as possible the chance of mind-over-matter—that is, the participant’s expectations interfering with the results—and reduces the chance of one group being lower risk than the other, which might skew the results. However, there are cases where such a study is impossible. For example, if you want to compare the safety of hospital birth to home birth, how do you randomly assign participants to hospital vs. home? Even worse, how do you make both the participant and the healthcare provider delivering the baby unaware of which “treatment” (hospital or home) is being used? Obviously, the mother is going to know whether she’s in her own house! So there are limits to what double-blind, placebo-controlled RCT’s or other high-quality research can study; therefore, by extension, there’s a limit to what the Cochrane Collaboration can review.
However, whether the influenza vaccine actually reduces the incidence of influenza infection is not impossible to study, though it may be difficult to wade through the thousands of studies on the topic to weed out the poor quality, biased ones. With that in mind, what has the Cochrane Collaboration found regarding influenza vaccination? The most recent (2014) Cochrane Review on influenza vaccination in adults reported, “The results of this review provide no evidence for the utilisation of vaccination against influenza in healthy adults as a routine public health measure.” 
Why is this? There are many reasons, one of which is the relatively low incidence of influenza. The CDC explains, “ILI [influenza-like illness] is a nonspecific respiratory illness characterized by fever, fatigue, cough, and other symptoms. The majority of ILI cases is not caused by influenza but by other viruses (e.g., rhinoviruses and respiratory syncytial virus [RSV], adenoviruses, and parainfluenza viruses)… [or] bacteria such as Legionella spp., Chlamydia pneumoniae, Mycoplasma pneumoniae, and Streptococcus pneumoniae.” [19, para. 2] In the same document, the CDC concludes, “many persons vaccinated against influenza will still get ILI.” [19, para. 9] In fact, about 200 viruses can cause influenza and ILI . A Cochrane collaborator expounded on the CDC’s statement, explaining that during flu season, only 7% of the population suffers ILI (influenza-like illness), and of those only 11% are caused by influenza and concludes: “…evidence presented here points to influenza being a relatively rare cause of ILI and a relatively rare disease. It follows that vaccines may not be appropriate preventive interventions for either influenza or ILI.” [20, p. 3]
Another reason discussed is the high number of vaccinations that would be necessary to prevent a single case of influenza. The researchers considered the proportion of the vaccinated population that does not respond to the vaccine and subsequently gets influenza or gets a non-influenza ILI or has a vaccine reaction (which may include flu-like symptoms), any of which results in taking sick days from work, versus the proportion of the unvaccinated population that gets ILI (caused by influenza or not), which results in taking sick days from work, but obviously does not have a vaccine reaction because they were unvaccinated. Their conclusion was that so many vaccines would be required to prevent a single case of influenza and that there would be so many side effects and non-influenza ILI cases that the end result is no economic advantage (regarding the number of days lost from work versus the cost of the vaccine as regards financial cost and work days lost to illness due to or in spite of the vaccine) to vaccination. The summarized statement reads, “The preventive effect of parenteral inactivated influenza vaccine on healthy adults is small: at least 40 people would need vaccination to avoid one ILI case… and 71 people would need vaccination to prevent one case of influenza… Vaccination shows no appreciable effect on working days lost or hospitalisation…. The effectiveness of live aerosol vaccines on healthy adults is similar to inactivated vaccines: 46 people… would need immunisation to avoid one ILI case” .
Furthermore, statistics regarding influenza complications are likely incorrect. For example, “flu” is often billed as a major cause of pneumonia [e.g., 19; 21; 22] and the CDC lumps flu and pneumonia together in morbidity and mortality statistics [e.g., 23]. However, as reported in the British Medical Journal regarding CDC flu and pneumonia statistics, the vast majority of “flu and pneumonia” deaths involve only pneumonia (for example, 61,777 out of 62,034 or 99.59% in 2001) and of the remaining deaths attributed to flu (257 out of 62,034 or 0.41%), only 7.00% (18 out of 257 “flu” cases or 0.029% of all “flu and pneumonia” cases) were positively identified as influenza . Therefore, given the relative rarity of influenza-related deaths, it should not be surprising that the 2010 Cochrane Review found “no credible evidence that there is an effect [of influenza vaccination] against complications such as pneumonia or death” [25, p. 12].
Significantly, there are also serious issues regarding bias interfering with study results. For example, a Cochrane review of influenza vaccination in children found “Extensive evidence of reporting bias of safety outcomes from trials of live attenuated influenza vaccines [which] impeded meaningful analysis” . This also calls into question the validity of any claims of efficacy made by the companies producing influenza vaccines, or in studies of influenza vaccines, the majority of which are funded by the companies producing them. Furthermore, a meta-analysis or review, such as the Cochrane reviews, are only as good as the studies included in them and may be no more than a summary of the prevailing bias . This makes it even more surprising that the Cochrane Review of influenza vaccination in healthy adults found no overall advantage to vaccination considering that, by their own account, about 70% of the studies included in their review had pharmaceutical industry funding and a high risk of bias, 20% had an unknown risk of bias, and only 10% had a low risk of bias .
The results for children are a little more complex than for healthy adults, but it appears that vaccination against influenza is completely ineffective in children under 2 years; is effective for those over age 2, with the live influenza vaccine more effective than the inactivated influenza vaccine; and is of unknown safety in any age group . Interestingly, the Cochrane Review for influenza vaccination in children stated, “This review includes trials funded by industry. An earlier systematic review of 274 influenza vaccine studies published up to 2007 found industry-funded studies were published in more prestigious journals and cited more than other studies independently from methodological quality and size. Studies funded from public sources were significantly less likely to report conclusions favourable to the vaccines. The review showed that reliable evidence on influenza vaccines is thin but there is evidence of widespread manipulation of conclusions and spurious notoriety of the studies. The content and conclusions of this review should be interpreted in the light of this finding.”  In other words, even though their review found influenza vaccination to be effective in children over age 2, they caution that the results could be largely due to bias secondary to pharmaceutical industry funding, as discussed above.
The most recent (2010) Cochrane review on influenza vaccination in older adults found that there is no evidence to recommend vaccination against influenza in older adults, either .
Footnote 3: “Low” or “poor” responders to vaccination, which seems to be a genetic trait and therefore not correctable by repeated vaccination, are those who develop poor or low-level antibody responses to initial vaccination and weak responses to revaccination, and lose detectable antibody levels long before the antibody response is expected to wane. For example, one study demonstrated loss of detectable antibodies against measles within 2-5 years of vaccination . Low responders are estimated to make up almost 5% of the population in the case of measles vaccination . I am unaware of the proportion of the population thought to be low responders specifically to pertussis vaccination. The sources I’ve found typically examine response to pertussis vaccination in newborns (not practiced in the U.S.), response to only one pertussis vaccination without boosters (not recommended in the U.S.), or response to the whole cell pertussis vaccine (not used in the U.S.).
Non-responders to vaccination refers to people who do not develop any detectable antibody response in spite of receiving the vaccine and all recommended boosters to the vaccine. Although the proportion of non-responders to each vaccine probably varies significantly, non-response occurs in 5-15% of those receiving the hepatitis B vaccine  and one study of pertussis vaccination in 137 infants showed similar results, with up to 91% demonstrating an immune response to full vaccination, implying a non-response rate as high as 9% following complete vaccination , so pertussis non-response is probably similar to hepatitis B non-response at 5-15%.
As discussed earlier, those who responded normally to vaccination but have had their immunity naturally wane over time and those who have not been vaccinated at all are also susceptible to pertussis. I don’t think it’s possible to even guess at the number of people in the population whose immunity has waned, though guesses have certainly been made. The rate of the completely unvaccinated also seems to be difficult to determine. According to the CDC, about 94.1% of children aged 19-35 months in the U.S. had received at least 3 doses of the DTaP vaccine, but this figure includes children who received only the DT without the pertussis (aP) portion, and I could not find a figure for children who have received absolutely no DTaP vaccines . Therefore, knowing that most of the children reported as having received at least 3 doses of DTaP probably got at least one DTaP (i.e., a vaccine that included the pertussis portion), and that many children may have gotten one or two DTaP vaccines prior to stopping vaccination and therefore were not counted in the statistics in spite of having had some level of pertussis vaccination, 5% (and probably actually much lower) is the best guess I can come up with (understanding it is almost certainly inaccurately high) for how many children aged 19-35 months are completely unvaccinated against pertussis. It’s also definitely inaccurate to consider all completely unvaccinated children or adults to be susceptible to pertussis infection given that having had a naturally-occurring pertussis infection in the past may confer 30 or more years of natural immunity , meaning that the unvaccinated may not actually be in the “susceptibles” group. Then again, the same is probably true for the vaccinated who nonetheless developed natural infection. Furthermore, many people develop an appropriate antibody response to vaccination but still develop disease. So again, these are all just best guesses.
In summary, with potentially 5% of the population being non-responders to vaccination, 5-15% of the population being low-responders to vaccination, and 5% being completely unvaccinated, that adds up to about 15-25% of the population being susceptible to pertussis infection, not including those whose (vaccine-induced or naturally-induced) immunity has naturally waned or those for whom an appropriate antibody response is insufficient to confer protection. Then again, as mentioned once or twice in the DISCLAIMER at the beginning of this blog post, this post is really about the newborn’s susceptibility to pertussis related to cocooning, not the susceptibility of non-newborns.
Footnote 4: I mentioned that the introduction of the pertussis vaccine was followed by a sharp reduction in pertussis rates. While true, just so that I don’t come across as uninformed, I want to acknowledge what many anti-vaxxers point out: that the rate of pertussis was already in sharp decline long before the vaccine was introduced, and that the rate of decline did not change after the introduction of the vaccine . Just so you know, yes, I am aware of that, but stating that fact in the body of the post itself would detract from my overall point. Additionally, I have no interest in discussing that topic in this post because, as discussed in the DISCLAIMER at the beginning of the post, this is about pertussis cocooning specifically, not about pertussis vaccination in general. I’ll leave you to do your own research on pertussis vaccination in general and decide whether the TdaP is superior to the Td—or, I suppose, to no vaccination—for your purposes.
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16 July 2015: Noticed that all the links in the references were broken. Fixed all the links. Noticed that one link was missing (reference #32). Added link.