It’s taken 30 years and more than $565 million to make it happen: the first-ever malaria vaccine. The innoculation, called Mosquirix, is the first of its kind to fight a parasite and has the potential to transform the lives of millions of people living in malaria-stricken areas. An estimated half million people die from the disease every year, the majority children. Such deaths have fallen by 47% since 2000 thanks to better prevention methods, but many have been waiting a long time for a vaccine that could protect children better and earlier.

“So many diseases are so effectively controlled by vaccines that we forget their power,” said Moncef Slaoui, head of GlaxoSmithKline’s (GSK) vaccine division, who has worked on the vaccine for 27 years. “But, when children die too commonly, you realize that vaccines are transformational.”

Mosquirix reduced malaria cases by about 40% in clinical trials. More important, since a child can get malaria multiple times within a single year, the vaccine prevented 6,000 infections per 1,000 children vaccinated over four years. It’s no magic bullet, but it’s significant progress for a tropical disease that’s received relatively few research dollars from drugmakers. Glaxo views Mosquirix as a “first-generation vaccine,” said Slaoui, and is already working on an even more effective follow-up.

This article is part of Fortune’s Best in Business 2015 package of highlights and lowlights of the year in business, politics and the economy by the writers and editors of Fortune. To see the entire package, click here.