Kenya's Ebola case: does Ervebo, a licensed Ebola vaccine, protect against Bundibugyo? WHO says it is not known

Does Ervebo, a licensed Ebola vaccine, protect against the Bundibugyo virus that caused Kenya's first imported case this month? Nobody knows yet. Ervebo is licensed against the Zaire species of Ebola virus, and the World Health Organization (WHO) wrote in its outbreak notice of 28 August that "it is not known whether it provides protection against the Bundibugyo virus in humans". WHO's Ebola fact sheet says there is no approved vaccine or treatment for Bundibugyo virus disease.

Kenya's Ministry of Health reported its first laboratory-confirmed imported case on 6 October, WHO said in its outbreak notice of 8 October. The patient arrived in Nairobi on 3 October and died on 5 October. In the Democratic Republic of Congo (DRC), WHO recorded 8,728 confirmed cases and 4,205 confirmed deaths as of 6 October.

The vaccine is already in use there. The Ghana News Agency reported on 9 October that the Africa Centres for Disease Control and Prevention (Africa CDC) said on 8 October the DRC had received 70,000 Ervebo doses, and that 7,775 health and other frontline workers had been vaccinated as of 7 October under a compassionate-use programme. Euronews reported on 20 August that WHO said the DRC was set to receive 70,000 doses.

Ebola viruses come in separate species, and Zaire and Bundibugyo are two of them. National Geographic reported on 15 June that Ervebo is built on a weakened vesicular stomatitis virus that displays part of the Ebola coat, which is made of glycoproteins. A vaccine built on one species' coat is like a key cut for one lock: a similar lock may turn, or it may stick. National Geographic reported that about 35 per cent of the glycoproteins on the surface of the Zaire and Bundibugyo viruses differ.

The hope that it will work rests on animals. A 2011 study in the Journal of Infectious Diseases gave cynomolgus macaques a single dose of a vaccine built the same way, with a weakened vesicular stomatitis virus carrying the Zaire glycoprotein; 75 per cent were protected against Bundibugyo, the paper's abstract says. National Geographic reported that in 2013 an early Bundibugyo-specific version of the vaccine protected 100 per cent of infected monkeys. On 20 August WHO said "early laboratory and animal data" suggest Ervebo may give some protection, Euronews reported. Monkeys are a stand-in; they are not people in an outbreak.

WHO's Technical Advisory Group recommended on 7 August that Ervebo be prioritised for inclusion in a randomised clinical trial. WHO Director-General Tedros Adhanom Ghebreyesus said at a news conference in Geneva on 12 August: "We do not know whether this vaccine is efficacious against Bundibugyo disease in humans," the US health news site STAT reported. STAT described a proposed design in which known contacts of cases would be randomly given either Ervebo or a placebo. Euronews reported that WHO and its partners set aside 20,000 of the 70,000 doses for a Phase III trial and 50,000 for frontline and health workers.

That is the kind of trial that can answer the question. The US Food and Drug Administration describes Phase I trials as testing safety and dosage in 20 to 100 volunteers. Phase II looks at efficacy and side effects in up to several hundred people, and Phase III enrols 300 to 3,000 and looks at efficacy and adverse reactions. The Ghana News Agency reported that Phase Ib trials of Oxford University's ChAdOx1 BDBV vaccine, a Bundibugyo-specific candidate, began in Uganda on 6 October, following Phase Ia trials in Britain in July. A Phase I result can say whether a vaccine is tolerated. It cannot say whether it prevents Ebola.

Médecins Sans Frontières (MSF) and its research arm Epicentre have launched a separate Ervebo study, called BRAVO, in Bunia, Ituri province, to follow 20,000 frontline workers in Ituri and North Kivu, the Kenyan daily The Standard reported on 29 September. MSF deputy director of operations Dr Guyguy Manangama said, as quoted by the paper, that "even partial protection could help reduce severe illness and deaths", and added: "It is important to stress that this vaccine will not end the current outbreak." The Ghana News Agency reported that Africa CDC said vaccination under BRAVO had been suspended because of supply shortages.

Health Cabinet Secretary Aden Duale told diplomats in Nairobi on 8 October that 57 contacts of Kenya's first patient had been identified, that those already accounted for had been placed under monitoring and quarantine, and that health teams were tracing the rest, the government-run Kenya News Agency reported. WHO's fact sheet gives the incubation period, from infection to symptoms, as 2 to 21 days, and says early intensive supportive care, including rehydration and treatment of specific symptoms, can improve survival.

WHO advises against any restriction of travel to, or trade with, affected countries, it said in its 8 October notice. Preliminary laboratory results for a suspected case in Wajir County came back negative on 8 October, Al Jazeera reported on 11 October, citing the county governor.