Wednesday, August 10, 2011

The End of Chicken Pox?

Medical students are taught that chicken pox pox* are classically described as “dewdrops on a rose petal.”  How the textbook authors got from this:

to this:

is beyond me.  I suspect some dermatologist got a little carried away after taking a creative writing course.  Now, any Boomer mother would be able to diagnose chicken pox in her child without the use of a gardening manual.  But believe or not, there may soon come a generation of doctors who will be unable to diagnose chicken pox by sight alone – and that’s a good thing.  Why?  Because it means that the varicella vaccine is working.

Varicella zoster is the virus that causes chicken pox, and the vaccine has been given to kids in the U.S. since 1995.  The single-dose shot is about 85% effective in preventing chicken pox, and close to 100% effective in preventing severe cases (typically defined as a horrifying 500 or more skin lesions, or requiring hospitalization).  The journal Pediatrics recently published a report showing that the number of deaths due to varicella has dropped by almost 90%.  ("Near elimination of varicella deaths in the US after implementation of the vaccination program”)  In fact, the reduction in mortality exceeded that predicted by computer modeling when the vaccine first came out.

Now if you look at the vertical axis, you’ll see that the absolute number of deaths, even before the advent of the vaccine, has always extremely low.  Most kids who fall ill will do fine with a little chicken soup (or, in my family, chicken jook).  In EBM parlance, the number needed to vaccinate is 3 million kids in order to prevent one death.  But that’s not really why we get our kids vaccinated, is it?  It’s more to prevent the discomfort, inconvenience and lost productivity of a case of chicken pox.  Given that over 90% of today’s adults have been infected with chickenpox, and the 85% effectiveness of the vaccine, that’s a number needed to treat of about 2 to prevent human misery.  And that’s a pretty good number in my book.

One last observation:  Since 2006, pediatricians now give a second, booster dose of varicella vaccine.  The number of breakthrough infections with the 2-dose vaccine is even lower than with the 1-dose.  So if, in the future, your doctor fails to diagnose chicken pox in your child without ordering a blood test, don’t be too hard on him!

(*Sorry, I know that sounds like “woodchuck chuck.”)


  1. HI EBMMommy - Just found your blog and love the idea of a little reality check merged in with the science of medicine. I am 33 weeks pregnant and there is so much "advice" about the things that I should and should not be doing it makes me crazy! I try to be as rational as possible - asking "how does the risk of doing this or that compare to driving?" Because I don't think twice about driving, but am now supposed to fear so many other things that are so much less risky.

    Back to your post... I got shingles a few years ago, as did my step-mom and another good family friend. In my research about shingles I discovered that since we've started vaccinating kids against chicken pox, the rate of shingles infections has gone up dramatically. If I recall correctly, the rate of hospitalization and long term side effects of shingles is much more serious than for chicken pox. Basically, the increase in shingles was described as an unanticipated consequence of the chicken pox vaccine. I am definitely not anti-vaccine, but do wonder if we might be trading one disease for a more serious disease in this case.

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