Last Look: It’s been a about a year and a half since an outbreak of a novel strain of Ebola gripped headlines across the world. Originating in Africa, the disease spread widely through Guinea, Liberia, and Sierra Leone, with cases found in Mali, Senegal, and Nigeria, as well. Localized transmission of cases far from the initial outbreak (including Spain and the United States) fanned public fear and led to border shutdowns and sometimes drastic quarantine measures in Europe and the U.S.

In all, the lethal hemorrhagic fever had claimed more than 11,000 lives and prompted the World Health Organization to say that it was the most challenging outbreak it had ever faced before cases began to decline in Spring 2015.

Even while the number of cases began to diminish, the specter of a worldwide outbreak spurred new discussions on dealing with disease transmission and put Ebola vaccine testing on a fast track.

Second Sightings: More than in past outbreaks, the 2015 epidemic has given researchers insight into how the Ebola virus affects survivors of the disease. It was known that the virus could continue to live in the eyes, semen, and spinal fluids of those that had recovered from the disease, but most recently, doctors surprised were a Scottish nurse became critically ill with meningitis related to a previous Ebola infection.

“I am not aware from the scientific literature of a case where Ebola has been associated with what we can only assume as life-threatening complications after someone has initially recovered, and certainly not so many months after,” Jonathan Ball, a professor of molecular virology at the University of Nottingham, told The Guardian.

While the nurse, Pauline Cafferkey, is beginning to recover, her recent illness was a wake up call regarding the virus’s ability to reinfect the victim and what that could mean for transmission opportunities.

“We've always known that it wasn't completely over,” Daniel Bausch, an infectious disease expert at Tulane University told NPR. “There's always the possibility that whatever first seeded this outbreak, likely a fruit bat, is still out there. “So, we've always known that there was the potential for reintroduction from the wild. But I think more recently and with these data coming in, we're understanding that there's also this potential for reintroduction from persistent virus production in humans, most notably from sexual transmission.”

Sexual transmission of Ebola is rare and transmission from other bodily fluids of past victims is unheard of. It’s also important to note that Ebola isn’t known to lurk in the bodies of all survivors—some are thought to clear the virus entirely. Still, doctors are cautious about what Cafferkey’s relapse might mean in terms of public health and the reintroduction of the disease.

A Peek at the Future: The breadth of the 2015 outbreak will provide researchers with ample opportunities to study the ongoing effects of Ebola infection.

The U.S. National Institutes of Health has partnered with Liberia health officials to study survivor immunity and transmission in about 7,500 people. Research for Health in Humanitarian Crises has funded seven studies, including one that will investigate geographic spread and another that will look at behavioral factors in transmission. Numerous other research projects exploring vaccines, diagnostics, and antivirals are also in progress.