Why don’t we vaccinate against chickenpox?

A friend asked me the other day, “why don’t we vaccinate against chickenpox?”. It’s a fair question. Currently in the UK we vaccinate every child against measles, mumps, rubella, diphtheria, pertussis, meningitis, pneomococcal disease, and others. Chickenpox is usually a mild illness (I had it three times, shut up, that’s totally normal), but just like those other infections it can sometimes be very serious. A tiny proportion of people with chickenpox develop encephalitis or meningitis, and recently a young boy very sadly died.

So, why don’t we vaccinate? The answer isn’t straightforward, and to understand it properly you need to know a bit about chickenpox and shingles.

Chickenpox is caused by a virus called varicella zoster. The initial infection causes chickenpox, which involves the itchy spots, blisters and general poorly-ness that we all know. Generally the acute infection clears within a few days and the spots and blisters clear up within a week or two. But what about the virus? Sadly, it doesn’t leave the body when the rash does.

Instead, virus particles lie dormant in nerve ganglia, which are nerve roots found in or near to the spinal column. The virus sleeps happily there, doing absolutely no harm for many years, and kept in check by the immunity that we develop after fighting off the initial infection. Most people then go on to meet other people with chickenpox. Maybe your kids get it, or people you meet at work, or socially. However it happens, every time you encounter the virus your immune system gets a little refresher course in how to deal with it effectively, and those viruses sleeping in your nerve ganglia are effectively kept snoozing for a while longer.

But (oh, that but) eventually the viruses wake up. They multiply, as viruses do, and spread up the infected nerve until they reach the surface and cause symptoms. This new illness is called shingles (or sometimes herpes zoster); it mainly affects adults, and it ranges from mild irritation to debilitatingly painful. Every nerve ganglion serves a distinct area of our bodies, so the area served by the infected nerve develops a painful, itchy, blistery rash. That rash can cause chickenpox in people who have never been exposed, because it’s full of newly-hatched virus particles. Commonly the rash appears on the torso, but it can also affect the face, causing embarrassment as well as pain and discomfort. It an even affect the eyes, causing ophthalmic shingles. Usually people also feel generally unwell, so alongside the rash there’s headache, fever, and generalised yuck. When we bear in mind that shingles often occurs in people who are already run down – perhaps due to old age, stress, other infections such as HIV, or chemotherapy – we realise that this is potentially a pretty serious condition.

Usually that’s that; the rash clears up and everything’s fine. But sometimes even when the bout of shingles has resolved people can be left with a condition called post-herpetic neuralgia, which simply means pain caused by herpes zoster. NHS Choices sums this up well – it’s a painful, burning, itchy, throbbing or stabbing sensation. It can last for months and it can be absolutely debilitating for an unlucky few. Other complications are similar to those of chickenpox – pneumonia, encephalitis, and meningitis. When you consider that the people most likely to get shingles are already likely to be vulnerable, that’s pretty concerning.

So that’s all very interesting, but how does it relate to chickenpox vaccines? As alluded to right at the start of this post, regular exposure to people with chickenpox acts as a kind of refresher course to the immune system. It reminds our immune mechanisms that varicella zoster virus exists, and gives us the tools to fight it off quickly if it pops up – either in the environment or in our own nerve ganglia. If we started to vaccinate against chickenpox – as many parts of the world do, incidentally – entire generations of adults would lose this immunity boost, because our children, grandchildren and peers simply would not be catching chickenpox.

We would drastically reduce childhood chickenpox, but the price would be up to 50 years of more frequent cases of shingles. This rise has been clearly seen in the USA, where the introduction of routine chickenpox vaccination has led to roughly a two-thirds increase in the rate of shingles among veterans.

Is that a price worth paying? That’s not a simple question to answer. The last time they looked at the question in 2010, the UK’s Joint Committee on Vaccination and Immunisation thought that it wasn’t. The fact is that these decisions are never easy, and they have to be made to benefit the population as a whole, and not individuals. Is the decision not to vaccinate against chickenpox in the UK the right one? That’s not really answerable. But is it the best possible interpretation of the evidence we currently have? I think it probably is.