Dengue Vaccine Will Actually Cause Spike in Disease
According to a study conducted by researchers from Oregon State University and Clemson University (published in the journal Epidemiology & Infection), a vaccine would actually increase rates of dengue infection during the first few years.
“Our analysis suggests that if we develop and widely use a vaccine for dengue fever, there may later be spikes in the incidence of the disease that are two to three times higher than its normal level,” researcher Jan Medlock said. At times, as much as sevenfold, the study found.
Vaccination is not Immunization
The mathematical model used by researchers predicts infection patterns following vaccination. The computer program was designed to look specifically at dengue fever, but researchers noted that it may also be applicable apply to other diseases.
Mosquito-borne dengue fever affects about 50 million people each year, commonly in tropical and subtropical regions. The disease is rarely fatal. Being infected a single time does not confer lifelong immunity, because there are several different strains of the dengue virus. But a second exposure usually does the trick. In Thailand, for example, 80 percent of children have been infected with dengue twice and therefore developed immunity by the age of 11.
Vaccination Gives Less Protection Than Natural Immunity
A vaccine will provide some, but not complete protection. The problem is that it will interrupt the natural, fairly steady rate of infections among children, according to Medlock.
At some point, natural fluctuation in mosquito populations would expose these children to the disease again. Vaccinated children’s immunity is less than that of people who had actually had the disease, and this would create a surge in infection rates and deaths.
Researchers note that similar effects may have happened in the past, following the introduction of other vaccines.
Could vaccine make dengue more lethal?
Dengue fever infection rates actually appear to have increased following the introduction of genetically modified (GM) mosquitoes intended to combat the disease in a region of Brazil.
The mosquitoes are engineered to reduce mosquito population. Biologists and civil society groups warned that killing off dengue mosquitoes could actually increase prevalence of the disease over time, by removing people’s natural immunity. This already appears to be happening.
Another concern raised with the GM mosquitoes might also be of relevance to a dengue vaccine: The most dangerous form of the disease, dengue hemorrhagic fever, is most common in people who have had dengue fever twice, but with a long gap between infections. Artificially disrupting the natural rate of dengue infection, whether via GM mosquitoes or vaccines, may actually increase the most deadly form of the disease – dengue hemorrhagic fever.
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