This is unequivocally wonderful news — a vaccine that is about 50% effective at preventing severe malaria, the deadliest disease in human history.

The World Health Organization on Wednesday endorsed the vaccine, the first step in a process that should lead to wide distribution in poor countries. To have a malaria vaccine that is safe, moderately effective and ready for distribution is “a historic event,” said Dr. Pedro Alonso, director of the W.H.O.’s global malaria program.

Malaria is rare in the developed world. There are just 2,000 cases in the United States each year, mostly among travelers returning from countries in which the disease is endemic. The vaccine, called Mosquirix, is not just a first for malaria — it is the first developed for any parasitic disease. Parasites are much more complex than viruses or bacteria, and the quest for a malaria vaccine has been underway for a hundred years.

The vaccine isn’t perfect but it’s going to save at least tens of thousands of lives every year. And there’s promise of an mRNA vaccine.