Why do anti-vaccine folks like to talk about baboons so much?
“Did you know that a study showed that baboons injected with whooping cough vaccine became infected with whooping cough anyway – and silently spread the disease to other baboons for 35 days?”
Is it because baboons are used in the study of vaccines?
That’s part of it, at least when they can find a study where they can cherry pick the results to suit their needs.
The Baboon Study
Like most anti-vaccine talking points, this one about baboons, has some truth to it.
There was a baboon study with the pertussis vaccine and it found that previously vaccinated baboons could develop asymptomatic carriage of the pertussis bacteria after they were intentionally infected.
Here is where it is important to note that an infection is different than a disease.
The example that many people are familiar with is tuberculosis. It is common to have a TB infection without any signs or symptoms and to not feel sick. The only reason we know that they have TB is because they had a positive TB test.
Unfortunately, about 5 to 10% of these people with TB infections can eventually develop TB disease, with coughing, weight loss, night sweats, fever, and chest pain, etc.
It is kind of the same with the baboons in the study. Twenty-four hours after two previously vaccinated baboons were inoculated with pertussis bacteria in the back of their nose and trachea, an unvaccinated baboon was put in each of their cages.
The vaccinated baboons continued to have pertussis bacteria in their noses, which the researchers had put there, for up to 35 days. And they were able to eventually pass the pertussis bacteria to the unvaccinated baboons in their cages. Vaccinated baboons also became infected or colonized after they were put in a cage with an intentionally infected unvaccinated baboon.
“…animals did not cough and showed no reduction of activity, loss of appetite, or other outward signs of disease.”
Warfel et al on Acellular pertussis vaccines protect against disease but fail to prevent infection and transmission in a nonhuman primate model
The vaccinated baboons were infected, but they never did develop symptoms of pertussis.
What Does The Baboon Study Mean?
One thing that is for sure – the baboon study found that the pertussis vaccines work. Only unvaccinated baboons got sick with pertussis.
But does this study explain our current outbreaks of pertussis?
Are vaccinated people becoming colonized and then getting others sick?
I guess it is possible, but we are not baboons in a cage with other baboons. How would we spread a respiratory disease, even if we did become colonized with the bacteria, if we don’t have symptoms?
It may explain part of our outbreaks though.
If vaccinated people do commonly become colonized with pertussis bacteria, then they might very well test positive for pertussis even though they don’t have symptomatic pertussis disease. So when they develop a cold or bronchitis and are found to have a positive pertussis test, then couldn’t that test just indicate that they have a pertussis infection and not disease, even though something else is actually causing their symptoms?
That’s what we think happens with strep carriers, right?
That’s kind of what the baboon study found. All of the baboons tested positive, but only the unvaccinated baboons had symptomatic pertussis disease.
“Baboons vaccinated with wP vaccines exhibit a level of protection that is intermediate between convalescent animals and aP-vaccinated animals. They exhibit no outwards signs of disease and are initially colonized to the same high level as aP-vaccinated animals but clear the infection more rapidly.”
Pinto et al on Pertussis disease and transmission and host responses: insights from the baboon model of pertussis.
It is interesting to note that the baboon study also found that baboons who had received whole cell pertussis vaccines also became carriers. They just didn’t stay carriers for as long as the baboons who got the newer acellular pertussis vaccine. But since they were still carriers, if asymptomatic transmission is such a big problem, wouldn’t it have been a big problem back in the day when everyone got whole cell pertussis vaccines?
The Debate Over Asymptomatic Carriage
Most vaccines prevent the spread of disease.
Do the pertussis vaccines?
Most folks still think so.
“The baboon model pioneered by Warfel et al. is without question a game-changer, shedding light on the impact of vaccination on disease and infection. However, the view it affords is clearer with respect to immunity and pathology than with respect to transmission. We point out that the extrapolation of the possibility of transmission from vaccinated baboons in the laboratory to the probability of transmission from vaccinated humans in the population is unwarranted. More work is needed to elucidate the relative transmissibility of infections in vaccinated vs. unvaccinated hosts. The evidence adduced above suggests, however, that vaccination with aP must have a strong effect on transmission as well as disease.”
Matthieu Domenech de Cellès et al on Epidemiological evidence for herd immunity induced by acellular pertussis vaccines
Even the author of the baboon study has said that “We agree that these data should not be directly extrapolated to pertussis transmission in humans. Although baboons are >96% genetically similar to humans, there are likely differences in how the species respond to vaccination and infection. We also agree that aP-vaccinated infected people are likely less efficient at transmitting pertussis compared with unvaccinated infected people, although it is not clear to what extent.”
Others think that asymptomatic carriage of pertussis might behind a lot of our recent outbreaks. Or at least what helps them grow so large.
Still, it is important to remember that unvaccinated folks do play a role in these outbreaks too. In a pertussis outbreak at a Florida preschool, in which most kids were vaccinated, the outbreak was started by a vaccine-exempt toddler.
And we have seen this in many other areas and it has been confirmed by many studies. Whatever else is contributing to pertussis outbreaks, like waning immunity, they are also associated with vaccine refusal.
“Counties with higher exemption rates had higher rates of reported pertussis among exempted and vaccinated children when compared with the low-exemption counties.”
Imdad et al. on Religious exemptions for immunization and risk of pertussis in New York State, 2000-2011.
But what if the DTaP and Tdap vaccines do cause folks to be asymptomatic carriers?
Even if that is true, understand that these vaccines don’t actually infect you, making you a carrier. They just might not prevent you from becoming a carrier if you are exposed to someone else with pertussis. While that might be a good reason to develop a new and better pertussis vaccine, it certainly isn’t a reason to skip or delay your child’s vaccines now.
Remember that even with our current outbreaks, rates of pertussis were much higher in the pre-vaccine era.
What to Know About Vaccines and Asymptomatic Carriers of Pertussis
The role of asymptomatic carriers and pertussis is controversial, but it certainly isn’t a reason to skip or delay your child’s vaccines.
More on the Vaccines and Asymptomatic Carriers of Pertussis
- Study – Acellular pertussis vaccines protect against disease but fail to prevent infection and transmission in a nonhuman primate model.
- Study – Comparison of Three Whole-Cell Pertussis Vaccines in the Baboon Model of Pertussis.
- Making sense out of the baboon pertussis study
- Epidemiological evidence for herd immunity induced by acellular pertussis vaccines
- Reply to Domenech de Cellès et al.: Infection and transmission of pertussis in the baboon model
- Two Recent Studies on Pertussis
- Maternal vaccination with pertussis vaccine containing only one immunity-stimulating component provides protection against disease in baboon model
- What Is Wrong with Pertussis Vaccine Immunity? The Problem of Waning Effectiveness of Pertussis Vaccines.
- Sustained Transmission of Pertussis in Vaccinated, 1–5-Year-Old Children in a Preschool, Florida, USA
- Effectiveness of pertussis vaccines–science vs. lies
- Refuting another antivaccination lie about the pertussis vaccine
- Study – Asymptomatic transmission and the resurgence of Bordetella pertussis
- Study – Pertussis: Biology, epidemiology and prevention.
- Study – Pertussis: Where did we go wrong and what can we do about it?
- Study – Live pertussis vaccines: will they protect against carriage and spread of pertussis?
- Study – Comparative Effectiveness of Acellular Versus Whole-Cell Pertussis Vaccines in Teenagers
- Study – Pertussis disease and transmission and host responses: insights from the baboon model of pertussis
- CDC – Coughing up the Facts on Pertussis: Emerging Trends and Vaccine Recommendations
- The problem of waning pertussis immunity
- Effectiveness of pertussis vaccines–science vs. lies
- Study – Clinical presentation of pertussis in unvaccinated and vaccinated children in the first six years of life.
- Study – Impact of acellular pertussis preschool booster vaccination on disease burden of pertussis in The Netherlands.
- Study – Association Between Vaccine Refusal and Vaccine-Preventable Diseases in the United States: A Review of Measles and Pertussis.
- Study – Religious exemptions for immunization and risk of pertussis in New York State, 2000-2011.
- Study – Infant Hospitalizations for Pertussis Before and After Tdap Recommendations for Adolescents