The Dance of Travel Immunizations

by Andrew Stein

In medicine, I’ve always heard that it never hurts to get a second opinion.  But in the case of travel immunizations, more opinions may mean a little more pain because they usually mean more pokes in the arm by long, sharp, shiny needles.  That said, when I didn’t cry, I sometimes received some celebratory lollypops.  (I’m calling that the silver lining.)  I do appreciate everyone who helped me figure out what I needed, but almost every time a new person, such as my friend’s girlfriend’s mother’s cousins’ next door neighbor suggested I have some XYZ vaccination against a deadly disease that wasn’t worth taking the risk on, I usually followed through.  When I finally leave on this trip, I will have so many fabulous antibodies floating around in my blood, that only kryptonite from my far-away home planet will be able to get me.  And lucky for me, there aren’t many mosquitoes that carry said kryptonite.

All kidding aside, the world and especially its jungles can be a scary place when you learn about all the diseases you can get.  Let’s take one disease, which I will talk more about when it comes to shots and dosages, as an example of nature’s lethality to be Japanese Encephalitis (JE).  Of those infected with JE, the CDC reports that 1 in 4 dies and of those who live, up to half may suffer permanent brain damage.  So with a little math, I learned that 63% of those infected with JE die or have permanent brain damage.  Like that good neighbor of my friend’s girlfriend’s mother’s cousin said, it’s not worth the risk.

Most vaccinations are easy.  One poke and I’m done, and a week or two afterwards, I’m ready to make out—vampire style—with a mosquito carrying that disease.  But not all immunizations are so easy.  One example is JE, which I just finished detailing the dangers of.  Don’t worry because I’m only going to go into detail on this one vaccination.  Currently, there are two vaccinations available against JE in the US, and those are JE-VAX and Ixiaro.  To serve as a quick bio, JE-VAX is the older, been-around-the-block vaccine that has been well tested and well documented, while Ixiaro made itself known in 2009 with a similar profile and slightly higher geometric mean titer. I didn’t know what those three words meant until I looked them up either.  Essentially, geometric mean titer just correlates to how much of the antibody is actually flowing through the blood.  JE-VAX is a 3-dose series at days 0, 7, and 30, and Ixiaro is a 2-dose series spaced 28 days apart.  Big pro for Ixiaro is its one less poke!

For the juicier part of this whole discussion, I was left with 25 days to receive either of these two vaccinations, and neither fit in the right time span.  It was time to put my nerd herd hat on and hit the journals.  First thing was looking at what the difference really was between the two.  I found Tauber et. al.’s article titled “Safety and immunogenicity of a Vero-cell-derived, inactivated Japanese encephalitis vaccine: a non-inferiority, phase III, randomized clinical trial” from 2007 in Lancet.  Basically, the article described the new Ixiaro vaccine and compared it to the old JE-VAX vaccine using a blinded study.  And not to worry, even the Ixiaro patients still had to receive the 3 shots, so they remained blind to what they were receiving, and the middle shot was just saline.  Conclusion of the study was that they both work, and the new one works slightly better.

Back to not having enough time to complete either course of injections, I found a study that compared JE-VAX when it was administered in two ways, one taking the usual 30 days, and one taking only 14 days.  The article, found in the American Journal of Tropical Medicine and Hygiene from 1999 by Defraites et. al. had results that gave me a sigh of relief.  The difference between the two dosing regimens was the geometric mean titers that I mentioned earlier.  Those who received the 30 day regimen had higher titers at follow up time points.  What does that mean for me?  It could mean that I have slightly less immunity; although, this is only very slight.  More than anything, it will mean that my immunity will probably wear off faster than average.  That same Journal of Tropical Medicine article said this; I’m not just making it up.  I’m not planning on being in Southeast Asia more than a couple months, and I’ll remember to boost my immunity next time Asian jungles call my name.  Importantly, I now have a good chance of avoiding that intimidating 63% statistic for the small number who acquire the infection.  Science, for the win.