How Billions of Hacked Mosquitoes and a Vaccine Could Beat the Deadly Dengue Virus

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How billions of hacked mosquitoes and a vaccine could beat the deadly dengue virus:

Last month, a parade of vehicles wound its way through three cities in Brazil, releasing clouds of mosquitoes into the air. The insects all carry a secret weapon - a bacterium called Wolbachia that lowers the odds that the mosquitoes can transmit the dreaded dengue virus to humans.

These infected mosquitoes are the latest weapon in Brazil's fight against dengue, which infects millions of people in the country each year and can be fatal. A biofactory that opened in the town of Curitiba in July can produce 100 million mosquito eggs per week - making it the largest such facility in the world. The company that runs it, Wolbito do Brasil, aims to protect about 14 million Brazilians per year through its Wolbachia-infected mosquitoes.

That will come as welcome news for the Brazilian health officials battling the rapidly growing threat of dengue. In 2024, the country experienced its worst outbreak yet: with 6.6 million probable cases and more than 6,300 related deaths. This year's outbreak, although less severe, is also one of the highest on record, with 1.6 million probable cases so far (see 'Dangerous outbreaks'). And the problem is spreading. Argentina, Colombia and Peru also experienced record-breaking outbreaks in 2024 and have seen a sustained increase in cases in recent years. Across Latin America and the Caribbean, deaths from dengue last year totalled more than 8,400 and the global figure reached more than 12,000 - the highest ever recorded for this disease.

As outbreaks grow larger and the crisis becomes more urgent, the Wolbachia method isn't Brazil's only bet. A locally produced dengue vaccine is now awaiting approval by the country's drug-regulatory agency, and its health ministry expects to start administering tens of millions of doses by next year.

These twin advances offer some hope to other countries - in the region and beyond. Driven by forces such as climate change, mosquito adaptation, globalized trade and movements of people, dengue is becoming a crisis worldwide, with an estimated 3.9 billion people at risk of infection. As Brazil rolls out its armies of infected mosquitoes and a vaccine in the coming year, the rest of the world will be watching closely.

Currently, there is one main dengue vaccine in use around the world: Qdenga, licensed by the Japanese pharmaceutical company Takeda. The vaccine has been approved in many countries, including Brazil, which was the first nation to include it in its public-health system.

However, Qdenga's roll-out in Brazil is limited. The country bought nine million doses of the two-dose vaccine this year: enough to vaccinate 4.5 million of its population of more than 210 million. So far, Qdenga has been administered to children between the ages of 10 and 14, one of the groups most likely to end up in hospital after contracting dengue, together with older people. Its safety and efficacy have not yet been tested in adults aged over 60.

The main reasons for such a limited roll-out in Brazil are availability and cost. Even though Brazil secured Qdenga from Takeda at one of the cheapest prices in the world -around US$19 per dose - the cost is still high compared with other vaccines. And even in the most optimistic scenario, the maximum number of doses Takeda could provide by 2028 is 50 million - enough to vaccinate 25 million people. What's more, for people who have not had dengue before, clinical trials did not show Qdenga to be effective against all four variants - or serotypes - of the dengue virus.

Brazil is trying to address all of those limitations with its one-dose vaccine candidate, developed at the Butantan Institute, a public biomedical research centre in Sao Paulo. "Having local production capacity gives us independence on decisions - how many doses we need, and at what speed to vaccinate," says Esper Kallas, Butantan's director. "You can practise prices that are more suitable and absorbable by a public-health system such as Brazil's."

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