A dengue fever vaccine created by Sanofi Pasteur has just entered Phase III trials, bringing the company closer to producing something that can prevent the disease than ever before. 

Dengue is not as well-known or widespread as pervasive diseases like malaria, but it infects several million people a year. Although restricted to the tropics, it is growing in geography and today has the potential to infect several billion people, according to the World Health Organization. 

The dengue fever vaccine is the latest in a long line of vaccines targeted at combating mosquito-borne illnesses, and Sanofi is placing a heavy bet that it will work. According to Reuters, Sanofi has invested over $400 million in making a manufacturing facility to create the vaccine in the event that it proves to be effective. Production would start in 2015 if all goes according to plan.

There are four other main competing vaccines but all are more unproven – in Phase I or II instead of Phase III trials like Sanofi’s – and so it would take around half a decade longer for them to come to market.

Creating a Dengue fever vaccine is complicated because there are 4 distinct types, all of which have to be accounted for in a vaccine, for it to be considered effective.