Tag: asymptomatic carriage

When is Shedding Season?

Have you heard of shedding season?

Shedding season is starting?
Shedding season is starting?

I’ll give you a hint, we aren’t talking about cats and dogs…

When is Shedding Season?

So it seems that some folks are really worried about vaccines and shedding.

Precautions against viral shedding? Was he giving out smallpox or oral polio vaccines?
Precautions against viral shedding? Was he giving out smallpox or oral polio vaccines?

While some vaccines do actually shed, it is really only the oral polio vaccine and the smallpox vaccine that we get concerned about with shedding.

And even then, shedding from the oral polio vaccine would only be a concern for someone with an immune system problem. Since the oral polio vaccine contains an attenuated virus, if that attenuated virus shed to someone else, they wouldn’t get polio except in the very rare situation when the virus mutates. Instead, they would get protection against polio. That’s one of the benefits of using the oral polio vaccine!

Still, we don’t use the oral polio vaccine in the United States anymore.

Although the smallpox vaccine can shed, it is from the site of injection, where a scab forms in the days to weeks after getting vaccinated. Covering the site should prevent other people from getting exposed to shed virus and fortunately, this vaccine is only used in very special situations.

And the rotavirus vaccine sheds, but you just have to wash your hands after changing diapers to avoid this attenuated virus. Are you going to get rotavirus if you are exposed to an infant who was recently vaccinated? Infants who get the vaccine don’t get rotavirus, so why would you if you are exposed to them?

And other vaccines?

While some live vaccines might shed in very specific situations, like if they caused a rare vaccine-induced disease, they otherwise don’t shed. That’s why we don’t worry about most folks with immune system problems getting exposed to people who have recently been vaccinated.

Don’t believe me?

Every time there is an outbreak of measles, someone insists that it was caused by a vaccine strain of measles that was shed from someone who was recently vaccinated. How often is that true?

So when is shedding season?

Anti-vaccine folks consider the start of the school year to be shedding season, because that’s when they think kids get caught up on their vaccines. Is that why we see big outbreaks of measles, chicken pox, and rotavirus at the start of the school year?

Oh wait, we don’t…

“Live vaccine virus shedding is a possible source of transmission of vaccine-strain viral infection but how frequently that occurs is unknown. There is no active surveillance of live virus vaccine shedding and most vaccine strain virus infections likely remain unidentified, untested and unreported.”

NVIC on The Emerging Risks of Live Virus & Virus Vectored Vaccines: Vaccine Strain Virus Infection, Shedding & Transmission

Despite the best efforts of anti-vaccine folks to scare parents about shedding, folks should know that this is no shedding season.

Cases of vaccine strain virus infections from shedding are unidentified and unreported because they don’t happen!

This is why some folks believe in shedding season...
This is why some folks believe in shedding season…

Do you need to teach your kids to fist bump instead of shaking hands during shedding season???

Think about it.

If there were a shedding season, then why wouldn’t there be more outbreaks? Because everyone has learned to fist bump and avoid shaking hands in school?

What to Know About Vaccine Shedding and Shedding Season

Shedding season isn’t a real thing.

More on Vaccine Shedding and Shedding Season

 

Can Vaccinated Children Be Asymptomatic Carriers of Pertussis?

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?”

Anti-vaccine Meme

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.

An adult male baboon.
An adult male baboon. Photo by Elizabeth Miller

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