The Chickenpox Vaccine and Shedding Concerns
Recently we received this question on our Vaccinate Your Baby Facebook page:
“My daughter and one of our friend’s daughters are the same age – 15months. I vaccinate, she doesn’t. She is trying to say that if my daughter gets the chickenpox vaccine, then it’s possible that she could give her child the chickenpox from shedding. My daughter hasn’t had the vaccine yet, but if she did, is that possible?”
The following response has been provided by Dr. Lara Zibners:
Firstly, well done on choosing to protect not only your child but the more vulnerable fellow humans she may come in contact with. Before we started routinely giving kids the chickenpox (varicella virus) shot, there were about 4 million cases annually resulting in about 100 preventable deaths every year. Think about that. Four million cases and only 100 deaths sounds pretty low risk, doesn’t it? Oh, wait, I forgot to mention the 10,000 hospitalizations every year. You know, for little things like serious skin infections, including the dreaded flesh-eating bacteria, bone infections, blood infections, pneumonia, meningitis, encephalitis, transverse myelitis, thrombocytopenia and stroke. Stuff like that. (I purposely threw a bunch of big words in there because they sound scary. And, to be honest, they are.)
Image of an unvaccinated child with varicella lesions in various stages. (Photo courtesy of the AAP)
So congratulations on making an informed and intelligent choice. I could go on and on about the risk to babies too young to be vaccinated, the truly devastating complications of varicella infection during pregnancy, and how time-tested and proven this vaccine is (clue: I’m pretty sure I was still wearing a diaper, at least at night, when it was first being tested. And in case you are wondering, I’m at an age where diapers are once again looming in my rapidly-nearing future). But, I won’t. Because that’s not your question. You already know that choosing to vaccinate your child against chickenpox means a 99% reduction in the risk of infection. Your question is whether a child who gets the chickenpox shot can infect another child. And that is a perfectly valid question to ask, I think.
So let’s back up for a second. Is this a vaccine that can cause an active infection? In other words, is it alive or killed? What I mean by that is some vaccines are absolutely 100% incapable of causing illness. These vaccines might contain a whole but very, very dead bug. Or it might contain just a small part of the bacteria or virus which conveniently happens to be the part that stimulates your immune system to develop antibodies against the actual infection, should it ever wander up your nose and into your body. The flu shot is an example of this kind of vaccine.
Then there are vaccines we call live-attentuated, meaning the actual virus is still alive, but it’s been altered so that it is very unlikely to cause an infection but will still trick the immune system into building up antibodies against it. The flu nasal spray is an example of this kind of vaccine. And so is the chickenpox shot. And because these vaccines carry a teeny tiny risk of infection, it is possible for your daughter to come down with chickenpox shortly after she has the shot. About 1% of kids do. The great news, however, is that these children develop very mild illnesses that usually lasts just a few days, is far less itchy and miserable, and is extremely unlikely to lead to any type of complication found in “wild-type” chickenpox infections. (“Wild-type” sounds really exotic, but it’s not. Just means you got it from the germy kid next door.)
Image of a breakthrough case of varicella on the back of a vaccinated child. (Photo courtesy of the CDC)
Now, let’s say your daughter was the unlucky 1% who got a very, very mild case of chickenpox after her shot. You might not even notice it because it could just be a few red dots on her chest that disappear in a couple of days. But let’s say she did. Now what is the risk to your friend’s unimmunized child? I am happy to tell you that the medical literature reports 5 such cases occurring over the course of 55 million doses of chickenpox vaccine injections. 5 in 55 million. And all of them were mild and without complications.
So, to summarize, let’s take out the old risk-balance sheet and see what we’ve got.
Unimmunized kid + wild-type infection: very real chance of serious illness and even death.
Immunized kid + wild-type infection: 95% protection against serious illness.
Immunized kid + a vaccine-related infection: rare with no serious complications.
Unimmunized kid exposed to your daughter after her shot: a miniscule chance of an extremely mild illness. And it makes perfect sense to me medically that if her daughter actually developed chickenpox, her immune system would kick into action, developing antibodies specific to the varicella virus. Which means at least some degree of protection against natural infection and severe disease.
Heck, with all that in mind, I say your friend should cross her fingers, buy some lottery tickets and hope it’s her lucky day! She should say thank you.
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