RIO DE JANEIRO, Brazil (AFP)—Brazil said Monday it was temporarily suspending use of the world’s first single-dose dengue vaccine following two suspicious deaths.

More than half a million people have received doses of the vaccine this year, which was developed publicly in Brazil and approved by health authorities in November.

It is the first single-dose inoculation against the mosquito-borne dengue virus, which can cause high fever, headaches, muscle pain, nausea and rashes, and in rare cases is fatal.

Of the 501,044 people vaccinated between January and May, 3,703 — 0.7 per cent — showed symptoms similar to dengue.

Forty-two people, meanwhile, had “more severe reactions,” according to the health ministry.

Authorities have recorded three severe cases, including two that resulted in the deaths of a 58-year-old man and a 48-year-old woman.

A 38-year-old woman entered intensive care but has since been discharged.

“There is not enough data to establish a cause-and-effect link between the vaccine and these three serious cases, but it is a warning signal,” Health Minister Alexandre Padilha told a press conference.

As a precaution, “we have decided to temporarily suspend vaccination,” he added, without elaborating on what would be required for it to be reintroduced.

The minister said the “absolutely unexpected” effects had not been observed during tests on over 16,000 volunteers across 14 Brazilian states.

Those trials had recorded an efficacy rate of 91.6 percent against the most severe form of the disease.

The only other dengue vaccine, TAK-003, requires two doses taken three months apart, according to the World Health Organization (WHO).

A single dose can help speed up and simplify mass vaccination campaigns.

Brazil recorded more than 6,000 dengue deaths in 2024 — nearly half of recorded deaths worldwide — but the situation improved significantly last year.