An Ebola quarantine in Sierra Leone. (European Commission DG ECHO / Flickr)

The last Ebola patient in all of Liberia was discharged from a treatment center on Thursday. And with that, the country was without a single confirmed case of the dreaded disease.

This is amazing. A few months ago, Ebola threatened to overwhelm the nation. Now, even though Ebola still exists in neighboring Sierra Leone and Guinea, Liberia is counting the days until it can be considered Ebola-free. That officially comes on April 4. Already, the celebrations have begun.

But Liberia has been here before, standing on the cusp of declaring Ebola gone, only to discover that the worst of the outbreak was yet to come.

Last May, Liberia and the rest of West Africa believed it was in a good position to defeat the disease. The small Ebola outbreak that had emerged in March 2014 and spread to all three countries appeared to be on its way out. No new cases had been reported in weeks. As June approached, public health experts believed the outbreak was over. Some doctors literally packed up and went home.

But just a couple days before the 42-day deadline was reached, Ebola returned. And this time, the outbreak turned into the world’s worst Ebola epidemic.

This is one reason that today public health experts are warning against complacency and repeating the mistakes of the recent past.

Ebola, after all, is a tricky disease. It emerges and disappears mysteriously. And the disease, without a cure and spread through close contact, kills most of the people who get it.

Tim Shenk with Doctors Without Borders said people need to remain vigilant even as they acknowledge Liberia's recent success.

“From the outset, this outbreak has been characterized by its unpredictability and geographic spread,” Shenk said in an email to The Washington Post.

Liberia shares a porous border with Sierra Leone and Guinea, where the capital cities of Freetown and Conarky have seen a recent spike in new Ebola cases.

"There are serious gaps that persist in the response," Shenk said.

Tracking the disease needs to be improved, he said, to ensure that Ebola doesn't slip into Liberia or the regions of Sierra Leone and Guinea where the disease was thought to be eradicated.

It's too early to celebrate. After all, that's what the world was doing last May, when Ebola appeared to be in an even deeper retreat.

And that's when Ebola came back, worse than ever before.