If you live in a developed nation, you probably haven’t heard of dengue. That’s okay. Not very many people in your position have. On the other hand, if you live in a developing nation — and you keep up with the news — you have heard of dengue and how bad it is getting and how bad it can be. Yet the people in developed nations need to pay attention to this because the “band” of warm weather is expanding as global climate change happens. So countries like the US and Australia are seeing cases, and the area of transmission is expanding into Europe, like so:
That was in 2008. The band keeps expanding. It’s only a matter of time until the United States and Europe have endemic dengue, in my most humble opinion.
HAVE NO FEAR, VACCINES ARE HERE! (RIGHT?)
Two of the things about Dengue that you need to know is that it is a viral disease transmitted by mosquitoes, and that the initial infection with it is usually not symptomatic. It’s when you get infected a second time that you can develop severe disease. So you’ll have a lot of people in the areas indicated above who are “seropositive” (have antibodies) to Dengue but never got sick. It’s those people you have to look out for because they will get very sick when they get Dengue again, showing that disease severity is immune-mediated.
There was a paper recently published in the New England Journal of Medicine talking about a vaccine efficacy trial conducted in different settings in Latin America, places where Dengue is endemic (commonly found all the time). The vaccine is not about preventing infection. It’s about preventing severe disease. Bet you didn’t see that coming!
We usually associate vaccines with preventing infection and disease, but there is a difference between these things. You can be infected and not sick, as is the case with influenza for one to two days before you get symptoms. It’s a couple of weeks with hepatitis A and a few days with measles… And, as we learned recently, up to 21 days with Ebola. That is why those diseases are so infectious and not easy to control by just looking for sick people (or quarantines).
The dengue vaccine discussed in the paper works by placing the viral particles of Dengue (the ones that trigger an immune response) on the membranes of Yellow Fever viruses, at the same time taking away the ability of the Yellow Fever viruses from causing disease. The body makes antibodies against Dengue, and those antibodies linger around, waiting to be activated by the next infection. If that infection does happen, the person doesn’t get sick (but is still infected).
As you can probably imagine, saying — quite truthfully — that this vaccine will not protect against Dengue infection will really throw some people for a loop. It will also not reduce Dengue in the population. Mosquito control will do that. The vaccine is more like a stop-gap measure to prevent bad outcomes of the disease while other things come into place to control Dengue. This brings me to the next point.
TOO MANY QUESTIONS
Imagine that you’re a policymaker in one of those countries affected by Dengue. (Or you’re the governor of Florida in a few years, for that matter.) Do you spend your resources on mosquito control or on the vaccine, or both? Who do you vaccinate, everyone or just people at risk for bad outcomes? Do you screen people getting the vaccine to make sure they have already had Dengue infection previously so that the vaccine is not “wasted” on them? (Though it’s yet to be determined if the vaccine can “trick” the immune system into thinking that it has already been exposed.)
I would be lying to you if I said that I wouldn’t want to be in the shoes of the person (or persons) making those decisions. After all, that’s why I’m putting all this effort into a DrPH degree.
So what would you do?
René F. Najera, DrPH
I'm a Doctor of Public Health, having studied at the Johns Hopkins University Bloomberg School of Public Health.
All opinions are my own and in no way represent anyone else or any of the organizations for which I work.
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