A small study published last Wednesday sparked hopes that the United States’ National Institutes of Health (NIH) had succeeded in creating a single-dose vaccine that would be 100 percent effective against dengue. Before you get too excited, the vaccine is only in Phase II out of III, meaning that the vaccine won’t be available for at least another two years. The Phase II results were based on a sample size of 41 participants, with only 21 of them receiving non-placebo vaccine TV003.
French pharmaceutical giant Sanofi Pasteur beat the NIH to the punch just this past December with the aptly-named Dengvaxia. The three-dose vaccine regimen is currently on the market in Mexico, Brazil and the Philippines. Dengvaxia is a live vaccine to be dosed at 0, 6 and 12 months. Known scientifically as CYD-TDV, it underwent two Phase III trials in Latin America (with CYD15) and Asia (with CYD14) and included over 35,000 participants. At the first follow-up period, 25 months after the first dose, pooled results from both the CYD14 and CYD15 trials indicated 59.2 percent efficacy against dengue in general and 78.2 percent efficacy in participants that tested seropositive for previous exposure to dengue.
What this all means is that while the vaccine isn’t enormously effective against first exposure to dengue, it is significantly more effective at preventing severe dengue. The pooled results include participants younger than 9 years of age despite the fact that the vaccine is no longer indicated for this age group after Phase III trials; the vaccine’s efficacy in participants over nine years of age is slightly higher, at 65.6 percent. It’s also estimated that the vaccine reduces the chances of developing Dengue Hemorrhagic Fever (which is as bad as it sounds) by 93 percent. Sanofi Pasteur anticipates Dengvaxia becoming one of its top three products within the next five years, and production is approaching 100 million doses annually.
If Sanofi’s vaccine isn’t necessarily a golden bullet, it’s definitely better than nothing. That said, one of its major weaknesses lies in its three-dose protocol, which NIH’s vaccine would eliminate. Many of the areas most severely affected by dengue in Latin America and Asia are outside the reach of many public health institutions, rendering access to even single-dose vaccines complicated enough. For many, obtaining access to three inoculative doses over the course of a year simply isn’t realistic.
The World Health Organization (WHO) aims to reduce dengue mortality by 50 percent in 128 different countries by the year 2020. In countries where dengue is endemic, results have shown that vaccinating 20 percent of the population can reduce the dengue burden by 50 percent in five years. While several pharmaceutical companies from Japan, India and the US have thrown their proverbial hats into the dengue ring, many years of trials lay ahead.
Brazil’s Butantan Institute launched a 17,000-participant Phase III trial for the NIH’s TV003 vaccine in February, and another trial is scheduled to begin in Bangladesh within the next few months. The single-dose vaccine would be a major game changer, especially if its 100 percent efficacy rate holds true. Unfortunately, good things only seem to come to those who wait.
Just in case you’d forgotten, dengue is a mosquito-borne virus. It exists in four different strains and poses a health threat to approximately 40 percent of the world’s population. While first exposure to dengue is often either totally asymptomatic or limited to fever, rash, chills, and stomach upset, second exposure to dengue can cause major complications, including Dengue Hemorrhagic Fever. Dengue kills over 22,000 people every year, many of them children.