It has been six weeks since the last confirmed Ebola patient tested negative for the virus, according to the WHO report.
The source of infection for the latest outbreak had likely been exposure to infected bodily fluid from an Ebola survivor.
After having been declared free of Ebola in December, Guinea reported seven confirmed and three probable infections in March and April.
The country now enters a 90-day period of heightened surveillance to ensure that any new cases are identified before they can spread.
“We must continue to be vigilant to ensure that we rapidly detect and stop any new cases that may occur,” said WHO Guinea representative Abou Bekr Gaye.
In neighbouring Liberia, three new Ebola cases were reported in early April, with the last patient testing negative on April 28th.
If no new cases occur, Liberia will be declared free of Ebola by June 9th.
The WHO nevertheless lifted its global health alert on Ebola at the end of March, meaning the virus no longer constitutes a global health emergency.
The disease has killed more than 11,000 people in Guinea, Liberia and Sierra Leone since the outbreak began in December 2013.