New Delhi, April 24 -- A single-dose dengue vaccine developed by Brazil's Butantan Institute demonstrated 65% efficacy against symptomatic dengue over five years of follow-up and showed meaningful protection even in people who had never previously been infected - potentially clearing a critical barrier that has beset dengue vaccine attempt to date. The findings, published in Nature Medicine in March, hold promise for a disease that leads to thousands of deaths worldwide. Dengue infected more people in 2024 than in any year on record, with WHO receiving reports of 14.4 million cases - including more than 52,000 severe cases and 11,201 deaths - across more than 100 countries. India is among nations badly hit by the disease, with four serotypes co-circulate. Efficacy against severe dengue or dengue with warning signs in the Brazilian trial reached 80.5%. Protection was stronger in dengue-experienced recipients at 77.1%, compared with 58.9% in those with no prior exposure. The findings are crucial given the complicated history of dengue vaccines, including the suspension of the world's first licensed dengue shot after it was found to worsen disease in recipients with no prior exposure to the virus. Dengue is caused by four genetically distinct serotypes - DENV-1 through DENV-4. A vaccine producing uneven or incomplete immunity across all four serotypes could leave recipients in a more dangerous position than if they had received no vaccine at all. For India, the annual case burden runs into tens of thousands.al....