A nurse administers an injection on the first day of the Ebola-vaccine study being conducted at Redemption Hospital, formerly an Ebola holding center, on Feb. 2, 2015, in Monrovia, Liberia.
John Moore/Getty Images

As Ebola continues on its deadly path across West Africa, health officials are trying to contain the unpredictable outbreak while also testing treatments and vaccines. However, according to USA Today, researchers are facing another challenge: There may not be enough patients on whom to test the experimental vaccinations.

New cases of the deadly virus have shot up across Guinea while slowing down across Liberia, raising questions as to whether there will be enough patients in Liberia for vaccine testing. According to the report, doctors are diagnosing only three to five new cases in Liberia per week. In August the number of patients being diagnosed was 300 a week.

The decline of the outbreak has been so significant that, according to the news site, drug developer Chimerix in North Carolina has canceled its trial of the antiviral drug brincidofovir, which was given to some U.S. Ebola victims but never formally tested.

Of course, although the decline of patients is “welcome news,” as Michael Osterholm of the Center for Infectious Disease Research and Policy at the University of Minnesota told USA Today, the dip in numbers could make it more difficult to tell if the vaccines actually work because there would be too few patients for comparison.

Liberian vaccination trials began in February with plans to enroll 27,000 volunteers. Other trials are planned for Guinea and Sierra Leone.

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In Guinea the number of deaths linked to Ebola has doubled in the last month, going from 30 a week in January to 65 for the first week of February. Deaths also increased from 21 a week to 44. The disease, as the site notes, isn’t disappearing in West Africa and still runs the risk of spreading routinely within the region, like malaria, for an undetermined amount of time.

Doing vaccination trials in a tropical climate also presents problems with storage and keeping vaccines at an adequate temperature in villages that don’t have reliable electricity, USA Toay notes.

Read more at USA Today.