The Ebola virus outbreak that began in Uganda on September 20 after one case was confirmed in Mubende district the previous day has spread to at least 130 people (lab confirmed) and caused 43 deaths as on November 2. The increase in fatalities has in turn increased the case fatality rate among lab-confirmed cases to 33% (43/130); the case fatality rate was 26.5% (34/128) as on October 29. It is not the increase in case fatality rate alone that is causing concern — the deadly virus has now reached the capital city Kampala; the virus was restricted to the rural areas of Uganda since the outbreak began in September.
Difficulty in tracing
Compared with rural regions, the presence of the virus in Kampala city increases the risk of the virus easily spreading to a large number of people and the increased difficulty of tracing all the contacts. Thus, there is an enhanced possibility of the outbreak becoming bigger, particularly as the virus has already spread to school children — at least six schoolchildren from three schools tested positive for the virus and one child died as on October 28. Also, there is a risk of the virus spreading across borders, as the virus is now present in the capital city.
Unlike the large Ebola outbreak of 2014-2016 caused by the Zaire strain that started in Guinea and spread to two other Western African countries — Sierra Leone and Liberia — by July 2014, the outbreak in Uganda is caused by the relatively rarer Sudan strain. Uganda is facing a Sudan Ebola virus outbreak after a decade.
The Ebola outbreak of 2014-2016 which spread to over 28,000 people and killed 11,000 people allowed the testing of Merck’s vaccine through a ring vaccination strategy. Currently there are no vaccines available for the Sudan strain of the Ebola virus. The silver lining is that Merck has developed a vaccine specifically against the Sudan strain in 2015 and 2016 after the success with the vaccine against the Zaire strain.
Testing on monkeys
However, since there was no outbreak of Ebola caused by the Sudan strain till September this year, the large stock of vaccines against the Sudan strain now spreading in Uganda was never tested on people. But the virus was tested on monkeys and was found to be effective in protecting against the virus. Jon Cohen of Science recently reported that Merck had, in 2021, destroyed the candidate vaccine that it had in vials as the vaccines had expired. However, the vaccine stored in bulk was found to be viable despite more than six years after they were produced.
Besides Merck’s vaccine for the Sudan strain, two other vaccines by the Sabin Vaccine Institute and the University of Oxford are in the process of being produced for clinical testing. While Merck’s vaccine uses the VSV (vesicular stomatitis virus) platform, both Sabin Vaccine Institute and the University of Oxford use the chimpanzee adenoviruses to carry the virus protein into humans, much like in the case of the AstraZeneca COVID-19 vaccine.
Clinical trials using the ring vaccination strategy of administering the vaccine among the contacts might begin by mid-November. On October 26, Uganda Media Centre (the country’s official centre for public communications) tweeted that all three candidate vaccines would be evaluated.
Health Minister Jane Ruth Aceng Ocero said the initial plan is to test the vaccine on 3,000 contacts of 150 lab-confirmed cases within 29 days of contact. “The trial preparation has been concluded and we estimate that we may begin the trial in two weeks’ time,” she said on October 26 in a tweet.