Where to vaccinate?
So, to vaccinate or not to vaccinate? Partly based on these findings, the World Health Organization now recommends that large-scale vaccination should only be undertaken in areas of high dengue transmission, preferably where at least 70 percent of the population is seropositive—that is, having detectable levels of antibodies against the virus, indicative of a prior infection. While Dengvaxia will be available in Singapore, for example, the country’s low dengue seroprevalence, especially among young adults, certainly factored into the authorities’ decision not to roll it out nation-wide.
An alternative approach, say the study authors, is to screen individuals before vaccination (this could potentially be done with rapid diagnostic tests), and only vaccinate those who are seropositive. Although logistically more demanding, this targeted strategy would minimize severe disease and also be more cost-effective. Since the vaccine is so good at boosting pre-existing immunity, a single dose (rather than the currently recommended three doses) is likely to be enough.
Factoring in Zika
Dengvaxia first gained regulatory approval last December; since then, Zika has burst onto the world stage. Researchers have speculated that existing immunity against related viruses—including dengue and yellow fever—might enhance Zika infection, resulting in the neurological complications and fetal abnormalities now associated with that virus.
Several studies have now shown that antibodies against dengue can indeed enhance Zika infection—at least in cell lines. More research is needed to establish if this actually happens in humans. Such a phenomenon could severely complicate dengue vaccination, and it will be necessary to determine if vaccine-induced antibodies against dengue can enhance Zika disease.
Meanwhile, health authorities should use the dengue vaccine with care, and tailor their vaccination strategy according to the local epidemiology of the disease, say the authors of the Science study. Given the vaccine’s modest predicted impact on dengue burden, it will also be important to manage public expectations about its effect, they add.
This article is from a monthly column called The Bug Report. Click here to see the other articles in this series.
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Copyright: Asian Scientist Magazine; Photo: Carlos Reusser Monsalvez/Flickr/CC.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.
