The outbreak of dengue fever that has unfolded in Latin America over the previous three months is staggering in its scale — 1,000,000 circumstances in Brazil in a matter of weeks, an enormous spike in Argentina, a state of emergency declared in Peru, and now one other, in Puerto Rico.

It forewarns of a altering panorama for the illness. The mosquitoes that unfold dengue thrive in densely populated cities with weak infrastructure, and in hotter and wetter environments — the kind of habitat that’s increasing rapidly with local weather change.

Greater than 3.5 million circumstances of dengue have been confirmed by governments in Latin America within the first three months of 2024, in contrast with 4.5 million in all of 2023. There have been greater than 1,000 deaths to this point this 12 months. The Pan-American Well being Group is warning that this can be the worst 12 months for dengue ever recorded.

The quickly shifting illness panorama wants new options, and researchers in Brazil delivered the lone shred of fine information on this story with the current announcement {that a} medical trial of a brand new dengue vaccine, delivered in a single shot, had offered sturdy safety in opposition to the illness.

There are two current vaccines for dengue, however one is an costly two-shot routine, whereas the opposite can solely be given to individuals who have already had a dengue an infection.

The brand new one-shot vaccine makes use of reside, weakened types of all 4 strains of the dengue virus, and it was created by scientists on the Nationwide Institutes of Well being in the US. The vaccine was licensed for growth by the Instituto Butantan, an enormous public analysis institute in São Paulo, and Merck & Co.

Butantan will make the vaccine. It already produces many of the immunizations utilized in Brazil, and has the capability to make tens of hundreds of thousands of doses of this new one. The institute plans to submit the dengue vaccine to Brazil’s regulatory company for approval within the subsequent few months and will start producing it subsequent 12 months.

However that gained’t assist with this outbreak, and by the point the manufacturing gears up and a nationwide rollout will get began, it might not be sufficient to assist with the subsequent one, both; dengue usually surges in three- or four-year cycles.

And it gained’t essentially be of assist to the remainder of Latin America: Butantan will solely make the vaccine for Brazil. Different international locations within the area battling dengue must buy it from Merck, which has not stated what it plans to cost for the shot.

And there’s, after all, demand for a dengue vaccine past the Americas: mosquitoes are spreading the illness to Croatia, Italy, California and different areas that haven’t seen it earlier than. Locations used to dealing with delicate outbreaks now face record-breaking ones: Bangladesh had 300,000 circumstances final 12 months.

Dengue is often identified by the identify breakbone fever, after the excruciating joint ache it causes. Not all people experiences that ache: Three-quarters of individuals contaminated with dengue don’t have any signs in any respect, and amongst those that do, most circumstances resemble solely a gentle flu.

However about 5 p.c of people that change into sick will progress to what’s known as extreme dengue. Plasma, the protein-rich fluid element of blood, can begin to leak out of blood vessels, inflicting sufferers to enter shock or endure organ failure.

When sufferers with extreme dengue are handled with blood transfusions and intravenous fluids, the mortality fee tends to be between 2 and 5 p.c. However after they don’t get therapy — as a result of they don’t understand it’s dengue and don’t search therapy rapidly sufficient, or as a result of well being facilities are overwhelmed — the mortality fee is 15 p.c.

In Brazil, the present dengue outbreak is hitting youngsters hardest; these beneath 5 have the best mortality fee of any age group, adopted by these aged 5 to 9. Adolescents between 10 and 14 have the best variety of confirmed circumstances, in keeping with the Instituto Oswaldo Cruz, a nationwide public well being analysis heart.

As clinics started to be overwhelmed with dengue sufferers in January, the Brazilian authorities purchased the complete world inventory of a Japanese-made vaccine for dengue known as Qdenga. Public well being nurses are delivering it to youngsters ages 6 to 16, however there’ll solely be sufficient vaccine to totally vaccinate 3.3 million of Brazil’s 220 million folks this 12 months.

This massive nationwide effort will shield a number of million youngsters, nevertheless it gained’t contribute something to its herd immunity.

Qdenga will not be low-cost: It’s about $115 per dose in Europe and $40 in Indonesia. Brazil is paying $19 per dose, having negotiated a lower cost for its big buy.

Takeda Prescribed drugs, which makes Qdenga, introduced a deal final month with Organic E, a big Indian generic drug maker, to license and produce as much as 50 million doses a 12 months, a part of a race to speed up manufacturing. The Indian vaccine ought to value significantly much less. However Organic E is unlikely to have regulatory approval to promote it earlier than 2030; it’s a sluggish course of that includes transferring know-how, organising a manufacturing line and getting a brand new model of even a widely known product authorized by regulators.

Dengue prices Brazil at the least $1 billion a 12 months in well being care therapy and misplaced productiveness. And that determine doesn’t consider the human struggling concerned.

There are 4 totally different strains of the dengue virus, which complicate greater than the method of creating a vaccine: The possibly deadly type of the illness is extra frequent when an individual has a second an infection, with a distinct pressure than that they had the primary time. Qdenga protects in opposition to all 4 strains of dengue, and the hope is that the brand new Butantan vaccine does too, though the info launched to this point present it examined solely in opposition to the 2 sorts that had been circulating through the first a part of the trial; extra outcomes are anticipated in June.

Tens of millions extra folks may have been uncovered to dengue when this outbreak lastly passes. However they’re going to want that new vaccine extra urgently than ever.