The first vaccine to prevent dengue, DengVaxia, now has the go-ahead to market in Mexico. On December 9 the Federal Commission for Protection against Sanitary Risks, approved the tetravalent dengue vaccine to prevent disease in all four dengue virus serotypes for individuals living in endemic areas. Lyon, France–based Sanofi Pasteur completed phase 3 clinical efficacy trials in Latin America in late summer 2014 (Nat. Biotechnol. 32, 605–606, 2014). Dengue is caused by one of four related but distinct flavivirus serotypes spread by infected Aedes aegypti mosquitoes. No other approved vaccines or antivirals exist for dengue, the world's fastest-growing tropical disease. The World Health Organization estimates the virus causes 400 million infections each year. Observers raised doubts over the vaccine's prospects after a 20,000-patient trial in Central and South America resulted in 50%, 74% and 77% protection against serotypes 1, 3 and 4, respectively, but only 35% against serotype 2. The Mexican authorities' decision to grant marketing authorization is a historic milestone for Sanofi, that has been developing the vaccine for 20 years, CEO Olivier Brandicourt said.