New Uganda Sudan ebolavirus outbreak means FDA-licensed vaccine for Zaire ebolavirus cannot be used

On Sept. 20, the World Health Organization announced an outbreak of Sudan ebolavirus was occurring in Mubende district in central Uganda:

“The Uganda Virus Research Institute confirmed the case after testing a sample taken from a 24-year-old male. This follows an investigation by the National Rapid Response team of six suspicious deaths that have occurred in the district this month. There are currently eight suspected cases who are receiving care in a health facility.”

Importantly, the only FDA-licensed Ebola vaccine is a one-dose vaccine that is specifically for the “Zaire ebolavirus” (previously referred to as a separate “strain” or “species” of ebolavirus) that has occurred multiple times since 1976, including the 2013-2016 Ebola outbreak in West Africa and several recent outbreaks in the Democratic Republic of Congo, e.g., 2018-2020.

Will a different Ebola vaccine (referenced below) that requires two doses separated by two months, be tested for safety, immunogenicity and potential efficacy against Sudan ebolavirus in this outbreak in Uganda?

As the Sept. 20 WHO announcement states:

“While ring vaccination of high-risk people with Ervebo (rVSV-ZEBOV) vaccine has been highly effective in controlling the spread of Ebola in recent outbreaks in the Democratic Republic of the Congo and elsewhere, this vaccine has only been approved to protect against the Zaire virus. Another vaccine produced by Johnson and Johnson may be effective but has yet to be specifically tested against Ebola Sudan.”

In January 2020, a WHO Q&A on Ebola vaccines including the following description of this second vaccine that is notably given as two nonidentical doses two months apart:

“In May 2020, the European Medicines Agency recommended to grant marketing authorisation to a second new vaccine delivered in 2 doses called Zabdeno (Ad26.ZEBOV) and Mvabea (MVA-BN-Filo) for individuals 1 year and older. The vaccine is delivered in 2 doses: Zabdeno is administered first and Mvabea is given approximately 8 weeks later as a second dose. This prophylactic 2-dose regimen is therefore not suitable for an outbreak response where immediate protection is necessary.”