News of a "100% effective" dengue vaccine was heralded with hyped-up fanfare this week.
And while the shot, which appears to protect everyone who gets it from the mosquito-borne virus with just one dose, would be an amazing weapon against the disease, it's too early to say that with any certainty yet.
Researchers at the National Institutes of Health, Johns Hopkins University, and the University of Vermont developed the vaccine, called TV003, and they published their results March 16 in Science Translational Medicine. The shot is designed to protect against all four strains of the dengue virus.
They gave 21 people TV003, and 20 people a placebo. Then six months later, they infected both groups with a strain of the virus that doesn't cause severe illness.
Remarkably, no one in the vaccine group got infected, while everyone in the placebo group did.
This is great news, because if the vaccine is in fact 100% effective, it could prevent the millions (some estimates put it as high as 390 million) people who get dengue every year from ever contracting it. The virus typically causes headache, fever, and joint pain, but its more severe version can lead to bleeding, vomiting, and organ impairment. Severe dengue kills 22,000 people every year, mostly children.
Researchers hope to use a similar trial setup to test Zika vaccine candidates, which are desperately needed as that related virus sweeps across the Americas without a treatment option.
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But this dengue vaccine trial was small, and only what's known as Phase II. The vaccine still needs to show its true efficacy in a large Phase III trial, which is the final step before it could get approval to go on the market.
Researchers have started a Phase III study in Brazil that's aiming to enroll 17,000 people. It should take at least five years to complete, though the NIH says they plan to have some results in two years.
Either way, it will be a few years before the vaccine could go to market and start protecting people all around the world on a large scale.
Another important note that many news stories neglected to mention is that we already have a dengue vaccine on the market. French pharmaceutical giant Sanofi got Brazil and Mexico — two of the largest countries affected by dengue — to approve its vaccine, Dengvaxia, in December 2015.
Dengvaxia is the world's first dengue vaccine, but it definitely won't be the last. It's 66% effective at preventing children over nine years of age from being infected with the virus, and it requires three doses — a necessity that is unrealistic for many public health systems where the disease circulates.
Cameron Simmons, a microbiologist and immunologist from the University of Melbourne who has worked on dengue for decades, said in a September interview that he's not convinced Sanofi's vaccine will make a dent on the global burden of dengue anytime soon.
"Dengue will unquestionably continue to be a big problem that's not met by a good, widely available, easy to use vaccine for at least the next decade," he said. "It's the beginning of the first chapter of dengue vaccines."
Perhaps this promising TV003 vaccine could be the next chapter. But it's going to take a long time to write that ending.
