It's Been a Week Without Any New Ebola Cases in West Africa

For the first time in more than a year and a half, the countries hit hardest by the largest Ebola outbreak in history went an entire week without reporting a single new case of the deadly hemorrhagic fever, the World Health Organization confirmed on Wednesday.

Not a single person in Guinea, Sierra Leone, or Liberia tested positive for the virus in the week leading up to October 4, a feat collectively achieved by the countries for the first time since the World Health Organization (WHO) officially declared the outbreak in March 2014. The West African nations reported more than 28,400 total cases during a nearly two-year-long period that began in December 2013, when the first infection was reported in Guinea's forest region.

"This is the first time that a complete epidemiological week has elapsed with zero confirmed cases since March 2014," the WHO said in its weekly situation report published on Wednesday.

Related: The Race to Zero: Looking for the Last Ebola Patients in Liberia

It's a promising development for the region, where international organizations are continuing with their efforts to bring the outbreak to an end with zero cases, a state that must hold for 42 days after the last individuals with confirmed infections are released from the hospital. But WHO pointed out other factors that could complicate declaring the outbreak officially over, such as hundreds of "contacts" — people who interacted with Ebola patients — in Guinea and Sierra Leone who have gone missing.

"All contacts have now completed follow-up in Sierra Leone," the WHO said in its report. "However, over 500 contacts remain under follow-up in Guinea, and several high-risk contacts associated with active and recently active chains of transmission in Guinea and Sierra Leone have been lost to follow-up."

Problems with lost or disappearing contacts have plagued Ebola response efforts throughout the outbreak. When an individual tests positive for Ebola, teams of local and international health workers are deployed to identify anyone who may have come interacted with the person after the onset of Ebola symptoms. An individual is not contagious until the onset of Ebola symptoms, which include fever, vomiting, and diarrhea.

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A level of fear and distrust about Ebola and the people who work to combat the virus has persisted among the citizens of Guinea, Sierra Leone, and Liberia, and while these relations have improved since the virus first made its jump from an animal to a human in 2013, contacts fleeing or disappearing has remained a relatively common occurrence. As the number of cases drops though, closely monitoring contacts and any potential cases becomes increasingly crucial, WHO's Ebola response director Rick Brennan explained in a previous interview.

"The last mile is all about the detailed epidemiological fieldwork, which we could do once we got to those lower numbers: finding every case, going out to villages, finding each person who's sick, and finding each one of their contacts," he said.

Beyond the recent week of no new cases, Liberia has been free of Ebola since September 3 — the second time the country has achieved the 42-day all-clear mark. Guinea still has active cases in the country, but Sierra Leone is currently on its way to achieving that mark, with no Ebola cases recorded in the country since September 28.

Follow Kayla Ruble on Twitter: @RubleKB

Watch the VICE News Documentary The Fight Against Ebola here: