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Every year over 400,000,000 people are infected with dengue fever, some experiencing severe symptoms such as hemorrhagic shock, which may be fatal. Finally a vaccine may be on its way.

Dr. Anna Durban and colleagues at the Johns Hopkins Bloomberg School of Public Health in Baltimore in the United States have developed a vaccine covering four strains of dengue fever they have dubbed TV003. This is an attenuated live vaccine, that is, it is a vaccine that contains live virus modified to cause a less serious reaction in the recipient. Last year they tested the vaccine and a placebo on groups of volunteers. Six months after giving the shots, volunteers were exposed to the virus. In the placebo group, everyone developed viremia, with detectable levels of virus in their blood. Of the volunteers given the placebo, 80 percent developed a rash and 20 percent developed neutropenia, the destruction of white blood cells. None of the volunteers given the attenuated live virus developed viremia; the virus could not be detected in their blood. None of the volunteers given the actual vaccine developed a rash or symptoms of blood cell destruction.

The test at Johns Hopkins was just a phase II trial, and a broader phase III clinical trial is underway in Brazil. However, Dr. Durban's vaccine is not the first for dengue fever. Another vaccine with a serious problem was actually approved in Mexico earlier this year (2016) in Mexico, the Philippines, and Peru.

The Problem with Trivalent Vaccine for Dengue Fever

The vaccine approved earlier this year was a trivalent vaccine, effective against three of the four strains of dengue fever. Clinical testing confirmed that the vaccine was effective against those three strains of the virus.

The problem with a trivalent vaccine turned out to be that if you are vaccinated for three strains of the dengue virus and then you are exposed to the fourth, not only do you not have protection against that strain, it is more virulent. It causes far worse symptoms than if you had not been vaccinated at all. As long as mosquitoes in your location do not become infected with the fourth strain, you don't have a problem, but if someone who has been infected with the fourth strain outside your area moves to your location and then is bitten by a mosquito that in turn bites you, you can become extremely sick. A trivalent vaccine can be better than no vaccine in a dengue fever outbreak, but at some point you may need a second immunization with the tetravalent vaccine, covering all four strains.

What to Do If You Can't Get Dengue Fever Vaccine

Most people who come down with dengue don't develop life-threatening symptoms. If you get some of the symptoms of the first stage of dengue after you have been bitten by mosquitoes, then be on the lookout for symptoms of dehydration (dizziness, dry skin, dark urine). Treating dehydration, by drinking water with at least a small amount of electrolytes (juice or even sugar and salt), will reduce some of the other symptoms, especially headache.

Better yet, don't get bitten by mosquitoes in the first place. Wear long sleeves and long pants. Use mosquito repellant. Stay indoors when mosquitoes are especially active, at sunup and sunrise. Don't let water pool around your home. Dengue fever isn't treatable. Do what you can to avoid it.

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