The worst Ebola outbreak in history may be on the decline, but it’s not over. A recent case in Guinea has health workers rushing to the border of neighboring Guinea-Bissau, hoping to quell a possible outbreak there. 

While the world celebrated earlier this month when Liberia was declared “Ebola-free,” medical teams are still being dispatched to hotspots around West Africa. And now they’re worried the virus may have crossed a border.

“The risk of a new outbreak in the region is real, so we are preparing now to be ready should the worst happen,” Youcef Ait Chellouche, deputy head of regional Ebola operation at the International Federation of Red Cross and Red Crescent Societies (IFRC) said in a Wednesday statement.

The IFRC and the WHO have both  sent medical experts to Guinea-Bissau to prepare for a possible outbreak in the small West African country, which could be in danger after a possibly-infected person crossed over from neighboring Guinea.

Guinea, Liberia and Sierra Leone were the countries most affected by the outbreak, which has killed more than 11,000 people since March of last year.

There were no reported cases in Liberia last week. But there were three in Sierra Leone and nine reported cases in Guinea last week, according to the World Health Organization. One of the cases occurred in a border town called Boke, which had no reported cases of Ebola for the past 200 days. Even though it’s only a single case, the situation has health officials worried.

WHO Ebola Virus Reported Cases Guinea, Liberia and Sierra Leone May 26 The number of reported Ebola causes in West Africa is on the decline, but there continue to be reports from Guinea and Sierra Leone. Photo: World Health Organization

“Because of the proximity to Guinea-Bissau of the recent cluster of cases in the Guinean prefecture of Boke, a response team from Guinea-Bissau has been deployed to the border to assess points of entry,” the WHO said in a Monday announcement. “Investigations are ongoing to trace a contact who attended the funeral of a case in Boke, and who is thought to have returned to a fishing community in Guinea-Bissau.”

In total, Ebola has affected 27,049 people and killed 11,149, according to the latest WHO update. According to the Center for Infectious Disease Research and Policy, there are still more than 10,000 health workers on the ground.  The outbreak cost the three most-affected countries billions of dollars in economic losses. It has prompted health officials to incite major changes at the WHO to help fight future crises, and spurred research for a handful of Ebola vaccines and treatments from researchers around the world.