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Late the other night, I saw a TV commercial for Zostavax®, the vaccine for shingles. It opened with a picture of a man’s stomach emblazoned with large and grotesque pustules, allegedly from shingles. (The make-up crew for the commercial really outdid themselves.) Readers of Common Science® will know that I’ve never met a vaccine I didn’t like. So after being confronted with this man’s stomach, I wondered if I had been delinquent in getting my shingles vaccine and if I should hop in my car and head to the all-night vaccine clinic. Evaluating that question has turned out to be rather interesting and involves just the sort of multi-decade analyses and public health dilemmas that I enjoy writing about.

As usual, let’s start by reviewing the science. Both chicken pox and shingles are caused by the varicella zoster virus (VZV). You get chicken pox from your initial exposure to VZV. As I will explain below, shingles can arise decades later and, if it does, is from the same VZV infection that gave you the chicken pox in the first place. The symptoms of chicken pox are an itchy rash with blisters, fatigue, and often a low-grade fever. Chicken pox usually resolves in about a week. Children rarely experience complications, but getting chicken pox as an adult can result in neurologic damage or, in rare cases, death. Therefore, it has long been common practice for parents to intentionally spread chicken pox from child-to-child to protect them from getting a more serious case when they grow up.   Since chicken pox is very contagious and is spread by coughing, sneezing, and exposure to the rash, this process is nearly 100% effective.

Once you get chicken pox and recover, you are immune to new VZV infections. Let me provide some extra clarity on this point, as it will be important later. In a sense, recovery from chicken pox is not a full recovery. The rash goes away and you feel better, but some dormant virus remains in your body, more on that below. While your immune system generally can’t clear out this dormant virus, it can fend off any new VZV that it encounters. This is why you can only get chicken pox once.   Keep this dynamic in mind as we proceed.

I have fond memories of my own bout of chicken pox. My friend Mike got it first. Then my mom and my friend Todd’s mom brought us over to watch cartoons with Mike on the couch. Soon thereafter, my rash appeared and I got to miss a week of school, stay home and watch the Young and the Restless with my mom, and, as a result, learn all about betrayal, amnesia, and long-lost family members returning from the dead. Our mothers’ decision to expose us to chicken pox was a rational one, but it did open the pathway for us to get shingles decades later.

In most cases when you are infected with a virus and recover, the virus is completely eliminated from your body. As I mentioned above, with VZV, this is not the case. If you have had chicken pox like me, then you have dormant virus particles lurking about in nerve cells near your spinal cord. As you age, there is an increasing likelihood that the dormant VZV will reactivate and cause shingles. People who never had chicken pox cannot get shingles.

Shingles presents as a painful and irritating rash typically in a single stripe on one side of the body, which resolves in 2-4 weeks.   The rash from shingles sheds VZV virus particles in a similar manner to that from chicken pox. Therefore, if an adult or a child without immunity to VZV comes in contact with someone with shingles, then he or she is quite likely to be infected with VZV and get chicken pox. Twenty percent of people who get shingles develop neurologic pain that can be severe. Fortunately, 85% of these people report that the pain resolves within a year. But this still leaves 3% of people who get shingles with long-term symptoms.

The situation I have described above existed in the U.S. for many generations. Nearly all children got chicken pox, one third of whom developed shingles as adults, and a few of whom developed painful long-term neurologic pain. In addition, a relatively small number of adults got chicken pox. This equilibrium was disrupted in 1995 when the chicken pox vaccine was introduced in the United States. My recollection was that it was initially optional, but it is now a mandatory requirement for children to enter the school system. Like all vaccines, the chicken pox vaccine is not 100% effective. However, it seems to have created sufficient herd immunity such that chicken pox has been effectively eliminated as a childhood disease. My children are 14 and 16 years old and neither they nor any of their peers have had chicken pox to my knowledge. However, the introduction of the chicken pox vaccine has rather different implications for the children who get it and for the adults who had chicken pox when they were young.

If you get the chicken pox vaccine as a child and develop immunity to VZV, all is well. You will never get chicken pox and, consequently, you can’t get shingles. However, absent having a really expensive lab test done, you won’t really know if you have developed immunity. Therefore, if you get the vaccine but don’t respond, you may assume you are immune but then encounter the VZV virus, likely from exposure to someone with shingles, and develop a serious case of adult-onset chicken pox. This contrasts with actually getting chicken pox in which case you know you are now immune to new VZV infections.

This risk that non-responders to the vaccine will be exposed to someone with shingles will be elevated over the next couple of decades because cases of shingles are increasing. The reason for that is fascinating and requires a short discussion of the immune system to appreciate. First, let’s pick a virus – say, whooping cough. When you are born, you have no immunity to whooping cough. You can develop immunity either by being infected with the virus or by getting a vaccine for whooping cough. What developing immunity means is that your body “remembers” how to fend off that particular virus. If you are exposed to the whooping cough virus after having developed immunity, your body recognizes it and quickly gets rid of it. However, if too much time passes and your body is not confronted with the whooping cough virus, it may begin to forget how to fight it.   This forgetting process explains the need for getting boosters of some vaccines from time to time. Now let’s consider how this dynamic applies to VZV.

When you get chicken pox as a child you develop immunity to VZV. This immunity helps to keep the dormant virus particles which remain at bay for many decades. Exposure of adults to children with chicken pox provides an immunity boost by helping their immune systems to “remember” how to fend off VZV and thus helps to prevent their dormant VZV from reactivating. Since fewer and fewer children will have the chicken pox due to having received the vaccine, fewer adults will receive the immune-boosting effects of contact with them, and more of us will get shingles. Multiple studies have shown that this is already happening. Therefore, if you are an adult with dormant VZV in your nerve cells and find out that there is a child nearby with chicken pox, you should go visit them and watch some cartoons.

Given that you are unlikely to find a child with chicken pox you can consider getting the shingles vaccine, which was approved by the FDA in 2007. The shingles vaccine is a higher dosage version of the chicken pox vaccine, which is not surprising since they are both designed to combat VZV. For people aged 50 to 80, the vaccine reduces the incidence of shingles by 50%. For people over the age of 80, its effectiveness is somewhat reduced. Studies of the length of the effectiveness of the vaccine are ongoing, but current estimates are that it should remain active for seven years. Unlike the chicken pox vaccine, the shingles vaccine is optional, hence the late night commercials.

I find it interesting to contrast the deployment of the chicken pox and shingles vaccines in the United States with that in the United Kingdom. In the U.S. we deployed the chicken pox vaccine for children as soon as it was available, even though it was known that this would result in more cases of shingles for adults. The increased number of cases of shingles, in addition to being unpleasant for the sufferers, negatively impacts our economy due to an increase in both sick days and health care costs. In the U.K, they waited until both versions of the VZV vaccine were available, chicken pox and shingles, and are now deploying them in a coordinated fashion. They waited to make sure they could provide the shingles vaccine to their adults before removing the immune boosting effects of chicken pox-bearing children. Personally, I find the U.K.’s approach to be sort of inspiring. They were willing to allow their children to get chicken pox to help protect their elderly from shingles.

So, let’s return to the question from the beginning of this column. Should I go get the shingles vaccine? I’ve got VZV in my nerve cells, I turn 50 next January, and I have never encountered a child with chicken pox. Therefore, I am nearly certain that the answer is “yes,” and intend to ask my doctor about it during my next check-up. You should probably ask as well.

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