Here we go again. There have been some articles published in peer-reviewed journals which have caused the antivaccination cult to not only misinterpret the data (shocking), but then broadcasting another lie (more shocking) which could lead to lower vaccinations rates.
According to research, some individuals who have been vaccinated against whooping cough (Bordetella pertussis), with either the DTaP or Tdap vaccine (which also protect against tetanus and diphtheria), remain infected with the pertussis bacteria, although they are asymptomatic. This is been morphed into the internet meme that only those who have been vaccinated carry the disease. Or worse yet, that the vaccine causes the asymptomatic infection. Typical of pseudoscience, the vaccine deniers take a little bit of scientific fact, and mutate it into something that meets their own biases.
First, let me give you a bit of background about the disease and vaccine, so that you can have a bit more context on what we’re discussing. The original DTP vaccine, sometimes called DTwP, became available in the USA in 1948 and was critical to dropping the number of cases of whooping cough from 260,000 in 1934 to less than a few thousand per year in the 1990′s. The original vaccine contained what was called “whole-cell” pertussis (thus wP), which includes all of the antigens of the pertussis bacterium, partially because it wasn’t understood (and to some extent still not fully understood) which antigens on the bacteria actually induce the proper adaptive immune response to destroy a pertussis infection.
Unfortunately, during the 80′s and 90′s, rare side effects of the available pertussis vaccines were noticed. Whole-cell DTP vaccines were associated with several local adverse events (for example, erythema, swelling, and pain at the injection site), fever, and other mild systemic events (for example, drowsiness, fretfulness, and anorexia), although almost all of these events are common to almost any vaccination. More severe problems were infrequently observed including convulsions, which occurred in one out of 1750 doses, and acute encephalopathy, which was extremely rare, observed in about 0-10.5 cases per million doses. Because of the safety concerns (some of which were overblown by the nascent anti-vaccination movement of the time), scientists began develop a more purified version of pertussis component called “acellular” (which constitutes the “a” portion of the vaccines used in the USA, DTaP for children and Tdap for adults). The acellular version contains fewer antigens isolated from the pertussis bacteria, and those antigens included were assumed to be the most effective in eliciting an immune response (pdf, excellent and easy to read explanation on how vaccines cause immunity) against the disease. So in 1997, the Advisory Committee on Immunization Practices recommended the full switch from the whole-cell to acellular pertussis vaccine. Many patients were transitioned to the acellular version in 1991, and almost all children were immunized using the acellular version by 1999.*
As with all medical procedures, there are some adverse effects with the pertussis vaccines. Moderate adverse effects from the vaccine occur in about 1 in 10,000 (or even fewer) injections. The most severe effects, which may or may not be related to the vaccine since it’s so low, are in the range of 1 out of a million doses.
- 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
Using simple math, the risk of dying from the disease is 1-2 out of 100. The risk of a moderate adverse effect from the vaccine is 1 in 10,000, or 100X less. I’d rather deal with a few hours of fever in my child, than taking the risk that they die from the disease. It’s really simple math, though we’ve already shown that antivaccination lunatics lack simple math skills. They think a 1 in 10,000 risk of a vaccine-related adverse event is actually a 100% risk, while a 1 in 100 risk of death from a disease is actually a 0% risk. It must be new math or something.
But let’s review the article, and see what the science really says.
An article, published in November 2013 in the Proceedings of the National Academy of Sciences (USA), and reviewed in much more detail by Tara Haelle, used a baboon model (a primate that is relatively genetically close to humans, though not a great ape) to examine how the whole-cell and acellular versions of the pertussis vaccine are working. They found that:
- Baboons vaccinated with the whole cell versions (the older vaccine no longer in use) recovered from their infections twice as fast as acellular-vaccinated baboons.
- Baboons vaccinated with the acellular version could contract the disease from another infected animal.
- Baboons vaccinated with the acellular version could transmit pertussis to other unvaccinated animals.
OK, on the surface, this could be scary. First of all, it appears that the acellular pertussis vaccine is not as protective as the whole cell version. But, we already knew this, and it has been thoroughly discussed. But his study was done in baboons, and it may be difficult to state that what we learn about disease transmission and immunity in baboons and make some inference what that means to humans. However, it does provide us with evidence that it’s possible that being vaccinated against whooping cough is not a guarantee that it will prevent an asymptomatic infection, that is, an infection without any overt symptoms of the disease, like the distinctive cough.
This pertussis vaccination with asymptomatic infection has been identified as early as 2000 in Israel. In a report published in Emerging Infectious Diseases, researchers examined children in a day care center who had been exposed to a child who had died of whooping cough. Of the 46 children exposed (all of whom were vaccinated with the full series of 4 vaccinations), five were shown to have contracted pertussis, but only two of those were symptomatic for the disease.
So what do we know?
- We know that the effectiveness of the acellular version of the pertussis vaccine is less than the whole cell version. This does not mean that the current version of the vaccine is ineffective, and it certainly does not mean that vaccinated children are more susceptible to whooping cough than unvaccinated children. An unvaccinated child is 6-25 times more likely to contract whooping cough than a vaccinated child. Read that carefully–6-25 TIMES more likely.
- Children who are vaccinated against whooping cough have decrease severity and duration of the disease.
- There appears to be growing evidence that a small percentage of vaccinated children could be asymptomatic for the disease but still pass the infection to others. This does not mean that all vaccinated children are “carriers” of pertussis. In fact, symptomatic unvaccinated children are much better carriers of the disease.
- Finally, the vaccine itself does not cause the asymptomatic infection. The vaccinated child acquires the infection from another infected child (in the Israeli cases, a child that had a severe whooping cough infection, infected others), and some of those children are asymptomatic for the disease. The vaccine contains antigens, just cell surface markers, not the whole bacteria. Even the whole cell vaccine contained, in essence, ground up bacteria. There is nothing alive in the vaccine, so there’s nothing to transmit.
This all seems so ridiculously simple to me. There is no way to misinterpret the science, unless you have an agenda.
But what does this all mean?
- Most importantly, get your child vaccinated against whooping cough, because all of the evidence shows that the it is generally effective, and prevents a dangerous disease.
- Personally, I’d rather my child be vaccinated and asymptomatic for the disease rather than risk dying by not being vaccinated. But that’s just me.
- If asymptomatic and vaccinated carriers are really a thing (and not just some statistical anomaly), then that’s even more of reason for us to improve the herd effect and make sure that every child is vaccinated against pertussis.
- All of the above for adults too. Whooping cough is not just a disease for children, and adults can pass the disease to infants who have not been fully vaccinated.
I hope this is all clear. Simple math tells us that the vaccine is much safer than getting whooping cough. Simple logic tell us that asymptomatic carriers do exist, and they don’t become so because of the vaccine. Understanding this is so easy that a baboon could do it. If they could talk. Or read.
*A scientific side note–this is how medical science works. Scientific studies identified an issue, then medicine fine tuned their procedures and/or medications over time as more evidence becomes available as to the safety and effectiveness of it. Science-based medicine adapts to new evidence, especially when weighing real risks versus real benefits (not invented ones of either). If we didn’t proceed with science based medicine, doctors would still be using bloodletting to treat diseases. Nevertheless, even with the whole-cell pertussis vaccine, the benefits far outweighed the rare risks.
- Barlow RS, Reynolds LE, Cieslak PR, Sullivan AD. Vaccinated Children and Adolescents with Pertussis Infections Have Decreased Illness Severity and Duration, Oregon 2010-2012. Clin Infect Dis. 2014 Mar 14. [Epub ahead of print] PubMed PMID: 24633685.
- Klein NP, Bartlett J, Fireman B, Rowhani-Rahbar A, Baxter R. Comparative Effectiveness of Acellular Versus Whole-Cell Pertussis Vaccines in Teenagers. Pediatrics. 20 May 2013. doi: 10.1542/peds.2012-3836
- Long SS, Deforest A, Smith DG, Lazaro C, Wassilak GF. Longitudinal study of adverse reactions following diphtheria-tetanus-pertussis vaccine in infancy. Pediatrics. 1990 Mar;85(3):294-302. PubMed PMID: 2304782.
- Misegades LK, Winter K, Harriman K, Talarico J, Messonnier NE, Clark TA, Martin SW. Association of childhood pertussis with receipt of 5 doses of pertussis vaccine by time since last vaccine dose, California, 2010. JAMA. 2012 Nov 28;308(20):2126-32. doi: 10.1001/jama.2012.14939. PubMed PMID: 23188029.
- Pertussis vaccination: use of acellular pertussis vaccines among infants and young children. Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 1997 Mar 28;46(RR-7):1-25. Erratum in: MMWR Morb Mortal Wkly Rep 1997 Aug 1;46(30):706. PubMed PMID: 9091780.
- Rohani P, Drake JM. The decline and resurgence of pertussis in the US. Epidemics. 2011 Sep;3(3-4):183-8. doi: 10.1016/j.epidem.2011.10.001. Epub 2011 Oct 14. PubMed PMID: 22094341.
- Shapiro ED. Acellular vaccines and resurgence of pertussis. JAMA. 2012 Nov 28;308(20):2149-50. doi: 10.1001/jama.2012.65031. PubMed PMID: 23188034.
- Srugo I, Benilevi D, Madeb R, Shapiro S, Shohat T, Somekh E, Rimmar Y, Gershtein V, Gershtein R, Marva E, Lahat N. Pertussis infection in fully vaccinated children in day-care centers, Israel. Emerg Infect Dis. 2000 Sep-Oct;6(5):526-9. PubMed PMID: 10998384; PubMed Central PMCID: PMC2627963.
- Warfel JM, Zimmerman LI, Merkel TJ. Acellular pertussis vaccines protect against disease but fail to prevent infection and transmission in a nonhuman primate model. Proc Natl Acad Sci U S A. 2014 Jan 14;111(2):787-92. doi: 10.1073/pnas.1314688110. Epub 2013 Nov 25. PubMed PMID: 24277828; PubMed Central PMCID: PMC3896208.
- Witt MA, Katz PH, Witt DJ. Unexpectedly limited durability of immunity following acellular pertussis vaccination in preadolescents in a North American outbreak. Clin Infect Dis. 2012 Jun;54(12):1730-5. doi: 10.1093/cid/cis287. Epub 2012 Mar 15. PubMed PMID: 22423127.