Why the Ebola strain confirmed in Kenya has no licensed vaccine, and what is being tested

There is no licensed vaccine against Bundibugyo ebolavirus, the species of Ebola confirmed in a patient who died in Nairobi. Kenya notified the World Health Organization (WHO) of the case on 6 October. The only licensed Ebola vaccine, Ervebo, is made against a different species, Zaire ebolavirus. When the Coalition for Epidemic Preparedness Innovations (CEPI), a vaccine-funding body, announced funding for three Bundibugyo candidates on 1 June, it said none was in clinical development.

WHO's Africa office said on 6 October that the patient, a Kenyan citizen who fell ill in the Democratic Republic of the Congo, arrived in Nairobi on 3 October and died on the night of 5 October. Its statement said: "There are currently no approved vaccines or specific treatments for Bundibugyo virus disease, but candidate products are being evaluated in clinical trials."

Bundibugyo is one of six known species of Orthoebolavirus, four of which are known to cause Ebola disease in humans, Gavi's VaccinesWork site wrote on 23 July. The Star reported on 2 June that WHO said "Ervebo is not licensed for prevention of BVD and evidence on cross-protection to other Ebola virus species remains limited and inconclusive." Cross-protection means a vaccine guarding against a relative of the virus it was built for.

Gavi wrote that Bundibugyo "has caused at least two previous outbreaks before the current multinational outbreak", though Ebola and Sudan viruses have caused more outbreaks.

CEPI's 1 June announcement named three Bundibugyo candidates and the money it would put behind each. The International AIDS Vaccine Initiative (IAVI) would receive up to US$3.2 million to prepare a master virus seed stock, using the same rVSV platform as the Zaire vaccine. Moderna would receive up to US$50 million for preclinical work and Phase 1 trials of an mRNA vaccine, with manufacturing for Phase 2/3 trials prepared at the same time. The University of Oxford and the Serum Institute of India would receive up to US$8.6 million for a ChAdOx1 vaccine, the platform behind the Oxford/AstraZeneca COVID-19 vaccine. CIDRAP, the University of Minnesota's Center for Infectious Disease Research and Policy, reported the same three awards. "With Bundibugyo virus spreading rapidly and no licensed vaccines, every day counts in the race against this deadly disease," CEPI chief executive Richard Hatchett said in the announcement.

Oxford's candidate, ChAdOx1 BDBV, has moved first. Gavi reported on 23 July that a Phase 1 trial was recruiting 50 healthy adults aged 18 to 55 in Oxford to assess safety and immune response. The Serum Institute had manufactured and stockpiled around 620,000 doses, Gavi wrote.

WHO has also looked at whether Ervebo protects against Bundibugyo. WHO's 28 May guidance said existing studies "suggest possible partial heterologous immune responses, but findings are inconsistent and based primarily on small nonhuman primate studies and laboratory immunological analyses". On 7 August, Al Jazeera reported that WHO experts recommended Ervebo be "prioritised for inclusion in a randomised clinical trial". It cited the experts' finding that three of four non-human primates vaccinated with Ervebo survived the Bundibugyo strain, against one of four control animals.

EpiNews reported on 8 August that WHO said immunising contacts of infected people "raises no safety concerns", and that a vaccine specifically targeting Bundibugyo "remains the preferred option in the long term". WHO's 31 August guidance said Ervebo should be used only within research protocols, and that the available evidence was insufficient to show whether it gives clinically meaningful protection in humans.

The UK Health Security Agency's report for the week ending 27 September, citing a situation report from the DRC's Institut National de Santé Publique, gave 8,116 confirmed cases and 3,924 confirmed deaths in the DRC as of 27 September. WHO and the Africa Centres for Disease Control and Prevention declared the outbreak in Uganda over on 27 August; Uganda had reported 20 confirmed cases, including two deaths.

The Star reported on 2 June that Ervebo was partly tested in Kenya from 2016, when about 40 healthy adult volunteers took part in early safety studies in Kilifi County. The trials checked safety and immune response, not protection during an outbreak.

For the case in Nairobi, WHO's Africa office said screening at high-risk points of entry was at the core of the response, and that isolation units in 27 high-risk counties had been identified and assessed. Kenyan health authorities had listed 28 contacts, including family members and health workers who cared for the patient, and were tracing 23 passengers and four crew members from the same flight, it said. WHO's 28 May guidance said outbreak control should continue to rely on established public health measures, including "surveillance, contact tracing, clinical management, infection prevention and control, and community engagement".