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article imageDengue fever vaccine may actually increase prevalence

By Tim Sandle     Sep 11, 2014 in Health
Scientists caution that such dengue fever vaccines will probably cause temporary but significant spikes in the disease in the years after they are first used, according to a new report.
Although it might seem counter-intuitive, the first use of a vaccine can often lead to an increase in disease cases. This is the result of less-than-perfect vaccine protection and routine fluctuations in the populations of insects who carry the diseases.
The argument has been pout forwards by Jan Medlock, an assistant professor in the Department of Biomedical Sciences at Oregon State University. To reach this conclusion, Medlock deployed mathematical modeling to examine the quirks of infectious disease transmission.
The scenario put forwards is that at the beginning of a vaccination program the administration will slow the numbers of children getting the disease, but only for a while. This is partly because a dengue vaccine will not provide total protection against infection. Following this, when the naturally fluctuating mosquito populations reach an unusually high level, a disproportionate number of children will become infected in a short period.
A possible way to deal with this phenomenon, Medlock argues, is simply to vaccinate fewer people. This would cause higher numbers of people to get the disease in the long run but reduce the intensity of the spikes and the associated demands on a health care system.
It should be noted that making a predictive model is difficult. This is because the levels of disease will fluctuate based on such variables as location, climate, the efficacy of a vaccine, the numbers of people vaccinated, surges in insect populations, and other factors.
Dengue fever is a serious illness that affects about 50 million people a year.
Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles. In a small proportion of cases the disease develops into the life-threatening dengue hemorrhagic fever, resulting in bleeding, low levels of blood platelets and blood plasma leakage, or into dengue shock syndrome, where dangerously low blood pressure occurs. The disease is an area subject to considerable research, and much of this is orientated towards vaccine development.
This argument has been published in the journal Epidemiology and Infection. The article is titled “The introduction of dengue vaccine may temporarily cause large spikes in prevalence”.
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