RIO DE JANEIRO, Brazil — Brazilian health authorities announced a temporary halt to the deployment of the world’s first single-dose dengue vaccine on Monday, triggering precautionary measures after two unexplained deaths linked to the inoculation prompted safety reviews.
Developed through a public-sector initiative in Brazil and granted regulatory approval by national health bodies last November, the groundbreaking vaccine has already been administered to more than 500,000 people across the country between January and May of this year. As the first ever single-dose injection designed to protect against dengue, a mosquito-borne viral infection that triggers symptoms ranging from high fever, intense headaches, and severe muscle pain to nausea and skin rashes, and can turn fatal in rare severe cases, the shot was hailed as a major leap forward in public health responses to the disease.
Preliminary post-vaccination surveillance data shows that of the 501,044 people who received the dose in the first five months of the year, roughly 0.7 percent — 3,703 individuals — developed symptoms that mirror those of natural dengue infection. Brazil’s Ministry of Health further confirmed that 42 recipients experienced more intense adverse responses, with three cases classified as severe. Those three severe events include the deaths of a 58-year-old man and a 48-year-old woman, while a third patient, a 38-year-old woman, required intensive care admission before making a full recovery and being discharged.
Speaking at a public press briefing, Health Minister Alexandre Padilha emphasized that regulators have not yet compiled sufficient evidence to confirm a direct causal relationship between the vaccine and the three serious adverse events. Even so, he noted that the unexplained incidents represent a clear warning sign that demands immediate precautionary action.
“As a safety measure, we have made the decision to temporarily suspend all vaccination campaigns using this product,” Padilha stated, adding that the government would not outline a timeline for reintroducing the shot until further investigation is completed. The minister also pointed out that these adverse effects were “completely unexpected” — no similar severe reactions were observed during earlier clinical trials that involved more than 16,000 volunteers across 14 Brazilian states. Those same trials recorded a 91.6 percent efficacy rate for the vaccine against the most life-threatening forms of dengue, a result that positioned it as a transformative tool for curbing the disease.
Unlike the only other approved dengue vaccine on the global market, TAK-003, which requires two separate doses administered three months apart per World Health Organization (WHO) guidelines, Brazil’s single-dose candidate was designed to streamline and accelerate large-scale mass vaccination campaigns, a key priority for dengue-endemic nations. For context, Brazil bore the brunt of global dengue burden in 2024, recording more than 6,000 deaths from the virus — nearly half of all fatal dengue cases recorded worldwide last year. While public health outcomes improved significantly in 2025, the virus remains a leading ongoing public health threat in the Latin American nation.