The outbreak of dengue fever that has unfolded in Latin America over the previous three months is staggering in its scale — one million 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.

More 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 up to now this yr. The Pan-American Health Organization is warning that this may be the worst year 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 latest announcement {that a} scientific trial of a brand new dengue vaccine, delivered in a single shot, had provided strong protection against the disease.

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

The 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 National Institutes of Health within the United States. The vaccine was licensed for improvement 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 yr.

But 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 following 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 make the vaccine just for Brazil. Other international locations within the area battling dengue should buy it from Merck, which has not stated what it plans to cost for the shot.

And there’s, in fact, 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. Places used to dealing with gentle outbreaks now face record-breaking ones: Bangladesh had 300,000 circumstances final yr.

Dengue is usually recognized 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 light flu.

But about 5 p.c of people that develop into sick will progress to what’s known as extreme dengue. Plasma, the protein-rich fluid part of blood, can begin to leak out of blood vessels, inflicting sufferers to enter shock or have 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. But after they don’t get therapy — as a result of they don’t notice 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 very best mortality fee of any age group, adopted by these age 5 to 9. Adolescents between 10 and 14 have the very best variety of confirmed circumstances, according to the Instituto Oswaldo Cruz, a nationwide public well being analysis heart.

As clinics started to be overwhelmed with dengue sufferers in January, the Brazilian government bought the entire global stock 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 can be sufficient vaccine to totally vaccinate solely 3.3 million of Brazil’s 220 million individuals this yr.

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

Qdenga is just not low-cost: It’s about $115 per dose in Europe and $40 in Indonesia. Brazil is paying $19 per dose, having negotiated a cheaper price for its large buy.

Takeda Pharmaceuticals, which makes Qdenga, introduced a deal final month with Biological E, a big Indian generic drug maker, to license and produce as much as 50 million doses a yr, a part of a race to speed up manufacturing. The Indian vaccine ought to price significantly much less. But Biological E is unlikely to have regulatory approval to promote it earlier than 2030; it’s a sluggish course of that entails 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 least $1 billion a year in well being care therapy and misplaced productiveness. And that determine doesn’t have in mind the human struggling concerned.

The proven fact that there are 4 totally different strains of the dengue virus complicates greater than the method of constructing a vaccine: The doubtlessly deadly type of the illness is extra widespread when sufferers 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 up to now exhibits it examined in opposition to solely the 2 varieties that have been circulating throughout the first a part of the trial; extra outcomes are anticipated in June.

Millions extra individuals could have been uncovered to dengue when this outbreak lastly passes. But they’re going to wish that new vaccine extra urgently than ever.