As Kenya recorded its seventh Ebola case, the criteria used to determine when a country has successfully interrupted transmission are key to understanding how the disease is contained.
Declaring the end of an Ebola outbreak involves more than treating infected patients and ensuring that their contacts are monitored, as health authorities must also establish that human-to-human transmission has been interrupted.
According to the World Health Organisation (WHO), the key benchmark is 42 consecutive days without a confirmed or probable case after the last potential exposure to the final case.
“The acute phase of the outbreak is defined by the propagation of the virus within communities through transmission of the virus from one person to another. This phase will be considered to have been interrupted when no confirmed or probable Ebola virus disease (EVD) cases are detected for a period of 42 days since the last potential exposure, the last case occurred,” WHO said.
A monitor reviewing results of airport thermal scanners at the Jomo Kenyatta International Airport (JKIA), October 6, 2026.
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MoH
The period represents twice the maximum incubation period for Ebola and is intended to help establish that no ongoing transmission chains have been missed.
The countdown begins at different points depending on the final patient’s outcome, including after recovery has been confirmed through two negative Polymerase Chain Reaction (PCR) blood tests taken at least 48 hours apart, or following a safe burial in cases where the patient dies.
Throughout the observation period, health authorities are expected to intensify surveillance, actively search for suspected cases, monitor contacts, and maintain teams capable of responding rapidly to new alerts.
Testing suspected Ebola-related deaths in communities and maintaining infection prevention measures are also important parts of the response.
Even after the 42-day period ends and an outbreak is declared over, WHO recommends continued surveillance for at least six months, including testing people who die under suspicious circumstances in the community, while infection prevention measures and emergency preparedness plans remain in place.
WHO also advises continuing medical care and testing of Ebola survivors for at least 18 months after the last confirmed patient recovers.
These precautions are necessary because some cases can be missed, the virus can remain in survivors’ bodies for months, contaminated medical equipment can carry the virus for weeks, and new infections can emerge from animals in areas where Ebola is regularly found.
Therefore, WHO advises health authorities to communicate the end of an outbreak carefully, acknowledging the possibility of renewed cases while avoiding absolute descriptions such as a country being completely "Ebola-free".
Uganda is a recent example of the process, with authorities announcing the end of its Bundibugyo virus outbreak on August 27, after completing the required 42-day countdown without a new confirmed case following the discharge of its last patient on July 16.
In Kenya, the Ministry of Health confirmed a third case on October 16 involving a 65-year-old woman who was a close relative and primary contact of the first two patients; she had been quarantined since October 6 before developing symptoms and testing positive.
A day later, four more cases were confirmed, bringing the total number of cases in the country to 7.
The ministry said 127 of 130 identified contacts had been traced and quarantined, with efforts continuing to locate the remaining three, while maintaining that the risk to the general public remained low because there was no evidence of community transmission.
Red Cross Society workers wearing personal protective equipment gathered after handling the coffin of a man who died of Ebola.
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CNBC Africa