French drugs group Sanofi said Friday that its vaccine against dengue, a mosquito-borne infection that kills thousands of people around the world each year, could be launched in about four years. \"The vaccine could be available... around 2015,\" Jean Lang, head of vaccine development at the group\'s subsidiary Sanofi-Pasteur, told reporters in Bangkok. The launch date is dependent on regulatory approval in each country based on the results of trials. The vaccine is the first for dengue to undergo advanced \"Phase III\" clinical trials -- the final stage before the results are submitted for regulatory approval. About 4,000 children in the central Thai province of Ratchaburi, one of the worst affected areas in the country, are participating in a study that aims to establish the efficacy of the vaccine. Dengue causes severe, flu-like symptoms in about 50 million people every year, mainly in developing countries. There are four strains, one of which is a potentially lethal type. Dengue has reemerged in recent years as a serious public health threat in tropical regions. There is currently no treatment, cure or vaccine.