The problem is, the dengue virus exists in at least four serotypes (I think the official count is now five), and infection only gives you long-lasting immunity to that particular variety (you have a short period of immunity to the others, but that disappears). What's worse, dengue is one of the best-known examples of antibody-dependent enhancement (ADE): if you get infected with another dengue serotype after your first round, the chances of a severe infection go up rather than down. The antibodies produced against the original serotype actually make things worse the next time around by enhancing viral entry into immune cells.
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So what the world needs, clearly, is a dengue vaccine that's effective against all the different serotypes and can be given to people who haven't been infected yet. Late last year, Takeda announced clincial results for their vaccine candidate (Qdenga). That one needs two doses, three months apart, but it can be given to children who have never had dengue at all. The efficacy at one year after this protocal was 80%, and follow-up at 4 1/2 years showed 60% efficacy against infection (efficacy against severe infection/hospitalization was 90% and 80% at those two time points). And now comes word from Brazil of another vaccine (Butantan-DV), which shows a two-year efficacy of 80% after a single dose (a real advantage!) The Phase III of that one is still underway, but it certainly looks promising. Neither of these show any signs of the ADE problem.
From the article:
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